If you asked me a year ago if I was a short story writer, I'd tell you "no." I've written a couple back in my high school and college days, however I had grand epics just waiting for me to write them down. My stories couldn't be compressed into a word limit of under 10,000 words. Besides everyone knows that the short story market is dying. Short stories were a waste of my time. It was utter bullshit.
I wrote my first new short story in February. I wrote two, actually, Cold and The Tannerspeak Witch, over a handful of Panera visits while my son was visiting his grandparents. I didn't expect them to be great, just something that would show my skills enough to get into Clarion. That didn't happen, but those two short stories were the strongest things I had work-shopped since I joined the writer's group. Since then I've written three more stories with various success. 11320 words. That's nearly as much as I wrote all last year. And I've added words to my new novel, over 1400 of them (my ticker is a little off).
Having the small goals makes me more productive. And seeing a story finished makes me want to push further and write a new one. Add another scene to my novel, try a little harder.
I compare writing short stories to sprinting a 100 meter race and writing a novel to running a marathon. Just because you are good at one doesn't mean you will be good at the other. But either way you're an athlete.
Short stories are a microcosm of story. Mine tend to be under 5,000 words. Fitting everything in, keeping the world grounded, the characters real and telling a story is hard. In my novel I can waffle around a little. If I digress on magical theory for a paragraph or two, as long as I don't bore you to tears, it's alright. There's room to meander. Every word in a short story has to serve the story, build the character, the world or both. Applying that to my novel has made that work stronger.
I've been able to test out resolutions, dialect dialogue, world build for another novel, and poke all my weak spots to see where I can toughen up.
The biggest benefit to writing short stories is the immediate feedback.It's hard to critique a novel chapter when it's been three weeks since you saw the previous chapter, and in the meantime the author has rewritten the scenes, rebuilt the world and axed a character. I feel like I put better work and get better feedback (more helpful not necessarily more positive) with short stories. And I can put them in front of real editors. I'm up to 8 or none rejections now. But they are teaching me things. A few rejections have been personalized with specific reasons why the story isn't right. Most aren't. But each "not for us" is telling me that there is something to improve. And that knowledge is gold.
So even though there is a limited pro market for short stories. And even though writing a good short story will not guarantee writing a good novel or securing an agent or publisher.... it's worth it.