Thoughts on deleting member accounts

Just out of interest (am actually writing some documentation here) do you delete member accounts on request.

We do if people ask, but don't if the person doesn't ask. We used to regularly clean out accounts where people joined but didn't post, but weirdness we got people who hadn't posted in like six months asking where their accounts had gone. Even more strange we had people who had never posted complaining (and that is just strange imho)

So what do you do. Please no flaming in this thread it's an honest question.