It needs to be something that requires cooperation between party members, and something that offers enough of a reward (i.e. damage, enmity redirection) to be worth using.
For instance on Thaum, with any reasonably good gear/materia equipped, it is very easy to pull hate off tanks. You can either pace yourself (boring, but effective), or you could have another option that allows you help the tank do more damage and keep things under control at a damage/mp tradeoff.
EDIT: For the FFXI players, remember being 37ish and doing SATA+skillchain on the tank? The damage was good, and the tank had it much easier. The cost was cooperation between players.