Wouldn't certain areas be more prone to having a specific type of resistance? Say you're in some frozen cavern dungeon. You would expect to see lots of frost resistant mobs, so before beginning you'd spec away from frost and pick something else. Makes sense right? From the looks of it, this buff is intended for those doing champion/boss runs for items rather than someone going through a first clear where switching specs on the fly would be more necessary. Just my thoughts.