I don't usually write them but when I do, I write them as a sort of marker for a milestone. Since my short stories are usually 6+ months apart, I always compare my latest short story to the one before it, and see where I've improved/degraded.
In terms of improvement, I've gotten better at planning my stuff and shortening the word count. In terms of degradation, you can say my prose have gotten a lot drier, and that I'm starting to focus heavily on dialogue, and that every paragraph oozes at least some semblance of horny. If you fed a goat a page from my recent short story you could impregnate it.