Agreed. Especially if you're MT, tank stance is a must. It may mean a decline in your DPS, but you're the tank, not a DPS. Better to stay alive and prevent healers from dying than die due to being out of tank stance. I'm fairly new to tanking, but I like to have my tank stance on as much as possible for situations where the MT dies due to being out of tank stance. That way, no one can complain that the OT wasn't picking up the slack.