I find writing in a diary-style is the easiest way to write fiction. The format is the same as a diary, with each entry beginning with the date, then describing the feelings or events of the character up to that date.
One big disadvantage is that you can't give too much blow-by-blow of events or you break the format. Yes, someone might write in a diary, "And then Bill said ... and then I said ... and then we went to the park ..." But would anyway really write in a diary, "Bill entered the room. He saw Sally on the left and me sitting at the desk. He strolled casually over to Sally. Sally nervously brushed her hair ..." etc. There's lots of description that goes into the action of a story that would just seem very unlikely in a diary.
Big advantage: Very conducive to detailed discussion of the hero's thoughts and feelings. In a conventional narrative, this would look odd. But in a diary, it's expected.
Another advantage that occurs to me: You can lie. That is, if in a narrative style you said, "Bob was having an affair with Sally", and then later you say that in fact this never happened, that that was all just a mistaken idea that one of the characters had, the reader rightly feels lied to: You told him it was so and then later you told him it was not. But if you write, "Amy thought that Bob was having an affair with Sally", that pretty much gives away that it's a mistake. Oh, there are plenty of ways around this, but sometimes it gets awkward. But in a diary format, you can write "Bob is having an affair with Sally", and it's understood that this is what the hero thinks, which may or may not be reality.
The "diary entry" format is not very immersive. It's hard to give believably the most immersive parts of classic prose - following given events step by step, line by line, each breath, frown and smirk. It's all a retrospection from earlier events of the day, compressed into a diary entry format, so it's never this detailed. This alone would probably be quite enough to discourage most authors.
Next comes the matter of fitting it in. The (meta-)writer must be a type to write one, and simultaneously interesting enough to be worth reading enough. Combining these two in a whole novel formatted as a journal is rare.
The format is stifling and gives little in exchange for the cost. You need to have it planned out in time - where a novel skips two months, the journal needs a filler. Where the novel has the protagonist striped of all possessions and locked up, the journal needs them to retain the journal. Where the novel has them keep a deadly secret that can never be written, the journal can't have it written down, or it would show them as reckless.
Still, the format is liked and is common as "fast forward" mode, as day summaries, as a retrospection on last days of a deceased. It is popular and a very powerful tool, but rarely used on scale of full novel - a chapter, a section, a retrospection, something to break the pacing - it's common to interweave short scenes of very intense action with journal entries of days preceding the events. It's not nearly as rare as you believe, it's just usually served as a side dish, not the main course.
Another issue with diary-formatted fiction is that it may limit you to certain time periods and classes of society. While Victorian ladies often wrote copious diary entries and even passed the books around among their friends and family for entertainment (which would give such a diary a reason for detail and description), it's harder to imagine a modern working woman with so much spare time, and utterly unbelievable for characters from eras and locations that lacked time, literacy, or writing materials.
It also compels you to choose as your protagonist the sort of highly articulate, introspective person who would keep a diary. There's nothing necessarily wrong with this, of course.
An alternative to strictly-diary novels is to create a book from a mix of documents (newspaper clippings, letters, court reports, etc.) as Dorothy Sayers did in The Documents in the Case.
I think writing a story as a journal, or diary, can be somewhat liberating and fun actually. I wrote my first book (my only book) as a journal. I loved it. I actually had a great deal of fun, as I had to become the journalist; I was writing the journal as my main character. I became and experienced everything he did and wrote it to, and for my, fictional self.
I actually felt the emotional pain, and the loneliness, as well as falling in love. I 'felt' the cold breeze at the beach as I thought of what a jerk I was. It was great. In preparation I read other diariess: The Diary of Anne Frank, Flowers for Algernon, The Diary Of A Superfluous Man, and Dracula. I read them once then came back to them for ideas and counsel.
The only difficulty was that this story was a period piece — mid 1980s. So I had to verify that this Saturday was actually August 10th, and was this VHS tape actually out at that time, were those types of clothes in fashion then? A lot to juggle. It took a lot of time but I had fun nonetheless.
In general, I don't think there are any real upsides or downsides to writing anything. Just write your heart out. Love what you're doing, what you're crafting.
You're the main character, chronicling your thoughts and feelings. Expressing how you felt when you said something to somebody and what you thought about when they replied, and what you plan to do about it - or whatever. I do encourage you to read some or all of The Diary of Anne Frank; she writes to an imaginary friend. If you'd like a could send you my eBook, or download it for a buck on Amazon, and see how I handled it. It's called "Endings" by me, Roger Maxwell. Or again let me know what format you'd like and I'll email a free copy :0) [email protected]. I hope this helps.
I'm a novice looking at the same thing for my first shot at a novel.
Journal / Diary style seems very good for my personal voice and particularly for a story I wish to tell about scientific exploration and adventure. It also allows you to highlight emotions, feelings, reflections, etc. at different points of the story (assuming you have the in-story author writing an entry at a time instead of a lump-sum document at the end of the story).
The disadvantages can be tricky, I feel: yes, the blow-by-blow can be hard to convey, but perhaps more than that, the dramatic tension of interpersonal conflict is much harder to achieve without live dialog between two characters in conflict.
Imagine trying to tell the finale of Star Wars Episode III: Revenge of the Sith where Anakin and Obi Wan are locked in conflict as an after-the-fact diary. Maybe you can do it, but you're going to suck the emotion and tension out of the scene, not just because it's not live, but because we know that the writer is writing it after the fact and therefore must have survived.
Of course, I think diary style approaches can be very useful for twists by relying on either an unreliable narrator (omitting things - particularly about the narrator's own actions, exaggerating, lying, etc) or deceiving the audience about the nature or purpose of the diary / story, only for it to have a new meaning at the end of the story when accompanied by an appropriate twist ending.
I'm going to give it a shot, but I'm worried about two scenes of intense ideological opposition, and think I ought to research how other writers have solved this problem in their own works. I recall reading a few books where authors changed modes a bit and had the narrator say something like "What happened next happened very quickly, but I will do my best to describe it to you as it happened".
I don't see how or why that should be a problem, and because it's a diary type entry you could add more intimate thoughts that may not occur in a 'normal' fiction book.
