Occasionally, it feels easier to write individual scenes of a prose and later connect them somehow.
Does this method have any significant benefit and/or throwback over the regular "perpetual" way?
In any given plot, there are a number of scenes which are easier and more fun to write than most of the others. Which scenes those are will differ from writer to writer, because each of us has affinities to particular types of scenes. They may also differ within a single writer from day to day as our moods and interests change.
I personally refer to these scenes as "candy-bar" scenes and I turn to them when I am exhausted by the drudgery of fleshing out an outline in a linear fashion. They are the scenes which bring joy and excitement back into the daily discipline of writing. After "eating" through a candy-bar scene, I usually feel more focused and committed to the work. I then return to the earlier point where I left off in my linear writing, set my course towards the opening of the now written candy-bar scene, and get back to it.
Candy-bar scenes are my best defense against both writers block and new project infidelity. As long as I still have a few uneaten candy-bars waiting for me further along in the course I have plotted, I can usually get past writing obstacles which might otherwise derail me. Once I run out of those favored scenes, my chances for completing the work falls dramatically.
Every scene in your outline needs to either be written or discarded. If a story can survive without a scene, it should be dropped, but if not, you must eventually focus your attention and talent on getting it written (and written well).
Additionally, readers are fickle. Every scene should be your best work. If your standards change based on how much fun you are having during the writing, the quality of your finished work will suffer and your reader's attention may stray.
A hand full of beautifully written scenes strung together by apathetically written prose is tragic. It simultaneously testifies to its author's talent and to their lack of discipline; to their potential and to their lack of ability to reach that potential.
Does fragmented writing a bad practice?
Not on its own... But when mixed with...
...yes, fragmented writing hurts your chances of completing your best works and of winning the audience which your talent deserves.
In regards to the question: "Is writing in fragments bad practice?" I'd refer you to the answer for "How do you get to Carnegie Hall?"
Any writing you do will hone your skills as a writer. Fragments may or may not be a good method of crafting a novel, but taken on their own, each fragment you produce increases your grasp of the art of creative writing.
There are certain fields where it is possible to practice something incorrectly and regress (martial arts is a good example, but in that field there are practical considerations.)
While there are certainly practical considerations for the profession of writing, but it doesn't sound like you're not at that stage yet, so the best thing you can do early on is simply write, write, write then write some more.
In terms of benefits/drawbacks, I'd say wrestling fragments into a narrative arc that sustains the reader's attention might be harder, but by the same token it could result in an exciting rejection of conventional form. It partly depends on who you are writing for (your audience) and your goals (to sell lots of copies, or create the truest art--the two are usually in conflict, what is known as the "lowest common denominator";)
I think it's ok for the basic outlining phase and for the first couple of drafts, just to get your ideas down. If you lose momentum on a particular scene/chapter/whatever terminology you're using but do still have ideas on a different one, then in my view it's better to switch to that part you do want to write rather than try to force something out for the part you don't, or lose all motivation to write altogether. If it means you don't lose momentum then by all means switch from a scene you're not enjoying writing to one you want to write.
Having said that, if you keep doing that then you're going to end up with disjointed scenes, especially if you go back and write an earlier scene after writing a later one. You'll end up with later scenes that fail to make reference to earlier ones where it would be logical to do so, and then you're bound to get a disjointed mess.
Worse, if you keep putting off writing scenes you're not enjoying and adding new scenes instead you might never finish those scenes off at all. If they're pivotal to your story then that's very bad! While it's unlikely that the things that your story hinges on are also the things you're not going to have much fun writing it's a possibility.
For that reason I feel it's only a good idea to employ scene switching early in the process. Write what you want to write for the first draft and not worry about the order your write things in. Then you've got the basic story points you want to hit fleshed out, stop, read everything you've written from beginning to end, and write notes on how it gels (or more likely fails to gel) as a story. Use the knowledge gained for your later drafts, try to stick to a more linear story writing style and tie the individual scenes you've written together more tightly.
At least that's how I've been working. As with most other things when it comes to creativity it's all down to what you find works best for you personally. I've found that for me personally, once momentum is lost it's very difficult to get it back and all you end up with is another abandoned draft.
In Story, Robert McKee warns very strongly about the dangers of writing in scenes. His point is that what makes a story is its overall arc. Given a set of characters you have invented, each with a particular motivation and a set of values that shape how they pursue their goals, it is easy to put almost any combination of those characters in a room together and allow them to interact. That will create a scene (in both meanings of the word) and if you are a good writer and you have imagined your characters well, it may be a very good scene that reveals interesting things to the reader. But that does not mean that it does anything to advance the overall arc of the story.
A collection of individually great scenes that do not work together to create a satisfying story arc do not make for a compelling story. To make the overall story work, you will have to cut some scenes, modify others, and create some new ones. The danger McKee argues (and as a Hollywood story doctor, he has seen writers go through this pattern) is that the writer has certain scenes (their darlings) that they are particularly fond of. Those scenes, the writer decides, have to stay in. And so the writer writes some new scenes, but the purpose of those scenes is to steer the plot to those darling scenes that they can't part with.
This does not produce a satisfying story arc. In fact, it often makes the problem worse, because every new scene that is created in each rewrite has the potential to be a really great scene and to become yet another darling through which the writer feels compelled to steer the plot, thus making the story line more and more convoluted with each iteration.
To avoid this trap, McKee would argue, you must think in terms of your overall story arc. Where is this story going and what it the best way to take it there? Write the scenes that the story needs to get where it is going. Otherwise, prepare to ruthlessly slay your darlings.
Chalk it up to individual experience, but I find that if I'm having writer's block on one project, I'll either hop to another project (if there is one), or simply write a poem or a prose snippet. If I need to write to get into the flow of writing, then I simply write about something on my mind. it doesn't matter what it is. Eventually the creative juices start flowing and I'm able to return to the "main" project.
No-one can answer that for you but you, do you find that the end result justifies the practice? I can't write in fragments because they either A. don't fit when I come to stitch the whole together, usually because of incompatibilities of style, and I have to start again or B. they take on a life of their own and turn into new and different stories that may or may not relate to the original intention. But that's me that may not hold true for you, just like I can sit down and write thousands of words in a couple of hours but only once every couple of months, I have to seize on my inspirational periods when I can where a lot of people I know can sit down and write every day.
In earlier times, I wrote that way. I had an idea, I fleshed out that idea, and I wrote a scene around it. Then I got another idea. Guess what happened to the first idea....
There's nothing wrong with doing that, as long as you understand why you're doing that. If the goal is to get some practice in pulling ideas out of your head and putting them on paper, it's great. You pick the scenes you want to write because they're fun to write. We all have to start somewhere.
You asked about advantages and disadvantages. Here's the big disadvantage. By doing the fun scenes, you ignore the not-fun scenes, the ones that are hard to do. Hard scenes take more practice. Hard scenes are about boring things that you have to make interesting. That word somehow is usually a clue that hands will be waved, because you don't see a clear path from B to G.
If you want to write, you'll put a lot of fun stuff in the trunk. If you want to be a writer, you'll have to do some work. You and you alone decide whether this is a hobby or a vocation.
Despite all that, every writer is different. For some people, the easy-first method may be best. You have to find your own groove.