I have writer friends who never teach. "It uses the same part of the brain I need for my own work," they say. Or: "I can't stand to read all those unprofessional manuscripts." Or: "If I analyze fiction too much, I'll lose my spontaneous ability to create it."
I've never found any of these things to be true for me. Last night my SF class met for the fifth of our eight sessions this term. Even though I was having a reaction to a flu shot (headache, muscle soreness, slight fever), I still enjoyed the class. It includes people who have just finished their first story ever (hi, Pat) and those who have published in ANALOG and ASIMOV'S. I learn something from all of them. The beginners force me to think about the basic components of a story, and the pros force me to think about that all-important, and often elusive, dividing line between a story that's almost salable and one that an editor actually buys. All this thinking eventually helps me with my own rewrites, since I'm one of those writers whose first drafts are mad, unplanned plunges into the unknown, necessitating much rewrite. We use a Clarion-style critique circle, and both the students and I learn from each others' reactions to a given story, too. And since usual about half of each class are returnees, there's a comfortable number of critiquers who know what they're doing.
Teaching has another personal advantage, as well. I'm a full-time writer. That means I spend much of the day in a small study, communing with people who don't exist. Actual live people who like SF make a welcome change. Even with a flu-shot reaction.