We prefer the natural flow of the forum to be doing our job. If a thread loses interest, it slowly "dies" to other pages and eventually forgotten. No locking required.
Usually, (note, usually) , bumping threads disrupts this flow. Especially when people quote/answer to others in that thread who may or may not be around any more. It can confuse new readers as well.
Of course it all is a huge grey area when it comes to modding. We prefer people to remake threads on most forum sections. The exceptions are present when for example being in Rika & Nitori's section. The thread creators themselves are allowed to bump up old threads only if they have something constructive/informative to add.
Only new people who quickly want to get few random posts off usually bump up those threads. Which is odd because there are plenty other threads for that reason.
TL DR: Bumping up old threads is not preferred.