WS when it won't take hate off your tank resulting in lost MP from the healers. If the mob is at 2% HP and you're at 100 TP, save it. If the next mob is pulled at 100% HP, the tank has only used provoke once, and you're sitting on 120 TP, wait till you get 200 TP to WS. You have to keep the situation in mind. At higher levels though I guess it's cool to just blast away every time you hit 100.