If you are a paladin, you can cast Hand of Protection on a friendly player to stop them from capping a flag. This can be used for a few reasons, as I myself use it often in AB to get caps, even though it only really is successful if only one other person is attempting it. This of course isn't limited to AB, it could be EoTS or IoC or anything to do with flags. I'm not sure if this is an exploit, or just a clever use of game mechanics, but useful nonetheless.