Having a pointer lock implies that relative motion is also used. When refocusing on a mouselook application which the driver is using relative motion for, an absolute motion hardware input is sent because of handling the wl_pointer.enter event. This can result in an unwanted warp/jerk.
The need to handle enter motion isn't applicable to mouselook or cases where the pointer is locked because the application is drawing its own cursor while covering vscreen, so it can be ignored during pointer lock.