When you finish a story, say a short story, not really intending to publish. Do you go back and revise it or let it be, starting on another story?
It is almost always worth editing. Even if it's Murder She Wrote / Star Wars crossover fanfiction that there will never be a market to publish, it's still worth practicing the art of editing. You took the time to write the story in the first place. Why not craft the best story you can?
I think something that's often overlooked by inexperienced writers is that there are very different skill sets involved with writing a first draft, vs. repeatedly editing that draft into a tight, well-constructed story. It took me years of writing before I really began to see how vital editing is.
It's important to be more than a "first-draft writer". If you find yourself frequently writing a single draft of a story, then tossing it aside, you're missing out on half of the writing experience. I believe that developing skill at editing your work is considerably harder than getting good at writing first drafts. Don't miss an opportunity to practice.
Furthermore, if there is a market out there for your story, you may realize that after a few revisions, it's worth trying to publish after all.
I'll throw out the need for some space. I might not go right back to something, so, yes, I'd move on to another story. But that doesn't mean you abandon it completely. There's a balance you must strike. If you get stuck revising something to the point you can't work on something else, I don't see that as helpful.
Revisit the story later. You never know what you might find with a fresh eye.
There are some stories that are just there to get thoughts out of your head. For me, if it's a complete story and something that I have the slightest interest in after I have finished a draft, I'll revise it. It may not happen right away, but give it a while and go back for a revision.
My reasoning behind this is it helps with the stories you ARE intending to publish. If you can learn to cut out the stuff you don't need and find what is missing in every story you write, even ones you don't necessarily care about, the ones you do care about will be that much better.