Pretty much the scenarios which are hardest on us boxers is heroics/raids and arena.

As far as heroics go, the best composition seems to be: Tank + Healer + 3x Range DPS.
If the healer and the 3x DPS can be the same class, this makes it easier.
Ranged dps is a little easier in that they're not in melee range for cleaves and such. Also ranged toons don't turn on melee, which means they maintain follow if you need to move them.

Arena would not work at all, for multiple melee toons, as follow breaks when melee is started.

I suppose it will depend on what your goals are for your Pallies.