I only move a thread if I think there's a better place for it. Your thread, for example, had "crappie" in the title, and it was mostly about crappie fishing, so I moved it to the main forum. Occasionally, threads pop up in here that have nothing to do with bream fishing, so I move 'em. I'm not sure why that happens. Maybe people forget which forum they're in when they start the thread.
Also, I generally move "specific location" threads. For example, if somebody starts a thread titled "How's the bream fishing at Lake X" or "When do the bream go on the beds in _______ " (fill in the state of your choice), I move it to that state's forum. In my experience as a member for seven years and as the bream moderator for however many years it's been, the "specific location" threads get very few responses. Often, they get no responses. Why? I have no idea. They just don't. So, I move 'em to a forum where they might get more and better replies.
When I move a thread, however, I always leave a "permanent redirect", which means that if you click on the moved thread, it will take you to that thread in another forum. That way, the thread never gets "lost".