Yes. Locking on to a target is pretty much pointless since your movement speed is slowed. If you have to move for whatever reason, you are greatly hindered. When you start casting an ability, you will automatically face the target. The macro I am describing is not so you face the target in that purpose. What I'm describing is if the target starts moving and you are already in the middle of a cast. Once you start casting fire for example, your character will turn and face the target. Now since your attacks on BLM have longer cast times, if that mob moves in a way you are no longer facing it, your cast will be interrupted, losing a GCD. This isn't a big deal if you're in a dungeon, but if you're raiding, you want to output as much dps as possible, and losing any GCDs is a no no. With that macro, if I cast a spell, and the mob starts moving before my cast finishes, I will just spam the macro, and my character will continue facing the target the entire way while it's moving.