Depends on where the telegraph is, as if it's a cone, the tank can sidestep during the attack, then return the boss to the original position after the attack to keep melee dps in place. There are also telegraph attacks which physically move the boss. So, as stated before the boss's movement is only partially constrained by telegraphs. So for this example a good tank would move out of the way of the cone attack and then turn the boss back to the original position, and interrupt the attack which the boss physically moves in order to keep the melee dps in place. A bad tank on the other hand would move out of the cone attack and eventually keep rotating the boss in the same direction so melee dps has to move, and simply avoid attacks which the boss physically moves for.