Having that option seems like a bad idea. People will automatically use it without thinking. I am certain that good portion of that search is a waste, as I would assume that most searches are specific enough to aim for a particular forum. Also, I am sure that it is a rare event when someone intends to search “About This Message Board”, “Comments On Cecil’s Columns” and “Comments On Staff Reports”. I can, however, understand leaving the option when you search for all posts and threads started by a user.
It is a very easy matter to manually choose which forums you want to search, why not force people to do so?
I can think of at least one implementation where searching all the open forums would be faster than searching specific ones. It’s very unlikely that vBulletin does it that way, but it’s possible.
I very much doubt that ‘most’ searches can be unquestionably pinned to a specific topic. Not least because you’re forgetting ‘new posts’ and searches by username.
I still prefer a suggestion myself and others have made elsewhere, of the default search being for the previous fortnight, or the previous month, or whatever. Then, only people really wanting to dig about in antique posts will put that load on the server.
They were indeed disabled once upon a time. It was very unpopular and lots of us were simply repeating the same search for each forum, one forum at a time, which wasn’t saving the hamsters from much.
My thoughts on the matter: please don’t disable any search function. If you have to impose some kind of limits to save resources, increase the length of time between posts or something, but don’t mess with search!
But there is no need to search each forum individualy. You can choose multiple forums for a search. Just hold down Ctrl. and click on the specific forums that you wish to search.