If you PvP its alot easier to be ganked with 3 than 5. I ran a warlock and 2 shadow priests a few years back on a pvp server and any decent rogue would have me sapped and down to 2 before I even knew he was there, then just pop evade and do it all over again. Made it real hard to level, and with the fact that you can fly just about anywhere its gonna be more of an issue now than before.