I love flash because of the process. Doesn't matter if the story is 66 words, or if it meters into the short-story realm at 3000, and I've done both. You can learn to draft faster, and see the benefits of doing so. You can enhance your editing and writing with every critical pass. You can ship it off to a publisher and get a response back in weeks, instead of waiting 3 months on a literary agent to respond. You can publish and market your own work to spread your name and find people that like your writing style.
Don't know about you guys, but if someone really loves my story, I'm happy to give it away. I don't need the money, I have the job for money. I don't need recognition or someone at NYT telling me what they think. I just love it when my stories resonate with someone, and my flash pieces make it easy to find people who like my work. Should be in the toolkit for any author. For the people posting about how "long" it takes, try hammering out a story quick and putting it through 4 fast revisions. Time yourself, then give yourself the same time to put out an equally long piece with one draft. Compare the two. Just saying. Everyone has their own writing style, but myself, I'm constantly experimenting and changing. I will write standing on my head and balancing bananas on my toes if there's the slightest chance that I can learn a new writing trick. Flash lets you carry out those experiments without trying them for months on a novel. It's not just experimental story development, it's experimenting with different writing practices to find the tiny hints that will help you improve.