To say that you must use your abilities strategically is a bit misleading. In some fights some players will need to strategically use 1 or 2 of their abilities, sure. It never gets to the point where even half of your actions are decided by the course of that particular fight rather than just your regular rotation.

For a tank it's pretty much knowing when big hits are coming in a fight and preempting them with mitigation abilities (similar for healer) as well as when to stun/ silence certain abilities. Some fights will require more precise positioning and such as part of the strategy, but that doesn't really affect what abilities you use. Tanks also need to use provoke 'strategically' (as in, use provoke to keep the other tank from dying and he/she will hopefully do the same for you when the time comes).