I feel that fixing minor typos, adding bold to relevant parts etc, is a reasonably valuable exercise for questions/answers that have come in recently.
However, I am less convinced that this is a good thing to do for older questions. It causes them to go to the top of the active questions queue and clog up the picture of interesting recent activity. Clearly if there are serious flaws in older questions then they need to be addressed, but for minor typesetting issues I'm not so sure.
Clearly this is a personal opinion, and I don't want to discourage people who are trying to make a contribution to this site. I've been in two minds about whether to accept/reject such edits and I was wondering what other people think.