Boost is a main reason why WAR/MNK is such a good hate holding tank at low levels (amongst the extra HP you gather from the subjob). Well, at least I've only known of WAR's tanking at low levels, none of them are willing enough at higher levels to actually use what their AF is for and sub MNK. They all want to be damage dealers (don't really have anything against that).

I always had the mindset that WAR's were one of the most versitile melee jobs, but all they want to do is sub NIN and look cool with their axes. -_-;