Once you've built up enmity, you can coast a little bit in the halfway point of the fight if you're running low on TP. That said, berserk cooldown phase is a nice way of getting TP back, and you can still use things like Mercy Stroke (and I think Brutal Swing, which will deal damage even if the stun component won't work on the boss) which does damage while you can't use your other abilities at no TP cost.