Writing is a tricky beast. I think it is easy to become complacent with the knowledge we have and think it is enough.
"I know all about structure."
"I know all about POV."
"I know all about cliche plots."
"I know all about..."
But like any career path, it is the things you don't know that you don't know which can stagnate your growth. Like a scientist who fails to read the research papers of his peers. Bit by bit, you fall behind in your knowledge of new things that have been done, unexpected things, which may push your own writing to places you did not conceive. Bit by bit, you fall behind in knowledge of what has been done before, what the new cliches are, the new structures, the new POV twists, and so forth. Stagnation.
So read short stories. Read them first because you enjoy reading them. Read them secondly because even if you are unaware of it, your craft is changing subtly by the influx of new possibilities.
It also does not hurt to occasionally read only for the purpose of deconstructing the craft of another writer. Read over twenty paragraph openings to the latest anthology of best stories in your genre and see what makes them work. Read through twenty endings, twenty middles. Dissect twenty POV choices and how they affected the stories. Learn the why's behind each author's narrative choices and through your questions learn more about your own choices and how you can raise your craft higher.
-Michelle