One aspect of forums I've never understood is when its acceptable to necro a thread or not.

One the one hand, most forums have a rule about searching for similar topics before starting a new thread, and if someone has the audacity to ask a question that's been asked before the forum mafia will show up to complain about how it's been discussed already.

However, if someone does search for a topic, then makes a post on it, the forum mafia will show up to complain about necro bumping as well.

What exactly are people supposed to do?