The Lock-On keybind is Z by default, and I usually use it when fighting Saga System NPCs or when I grind using Shadow Dummies. You can lock onto other entities from pretty far away, and you can also use Instant Transmission really quickly when you’ve locked onto someone, so it’s really good for PvP most of the time (especially if your opponent likes flying around all the time and you can’t hit them without Lock-On).
Lock-On can be a bit buggy sometimes with the camera, but that’s only if you’re standing really close to the entity you Locked-On to.
Hope that helps.