One advantage to writing flash fiction is, by definition, you have to keep it short. There is no room for any waffle and it really does help focus the story. Flash fiction can be huge fun to write and I must admit I bless Scrivener's project targets as I can watch the bar graph change colour as I get nearer and then achieve my word count. I know it sounds silly but that traffic light colour change from red to amber to green really does keep me writing until I reach my target (which of course is the idea).
I haven't tried this yet (though I plan to at some point) but given a flash piece really has to be to the point, it in turn could be a useful starting point for a longer short story and, I suppose, eventually a novel too. I'm writing more flash fiction and find it a fun challenge to keep myself to a very low word count. I like 100 words flash pieces in particular (some I've written have appeared on Cafelit). The link takes you to one of my more recent published pieces. Hope you like it.