Regen is almost never needed.. And when it's needed you can throw it (as long as it's not before the pull), since the only time you really need it is either during a boss fight or when the tank is tanking a large group of mobs. As your group kill off the mobs, the need for regen will also go down and you can go over to casting cure1 or cure 2 without having regen up. That way, he'll never have regen up when he's/she's going for the next pull.
I barely ever use regen for trash mobs.