I find it useful because it gives me more control over the pick. Small muscles = fine adjustment, large muscles = coarse adjustment.
When I use an immovable trigger grip, all control comes from the wrist, elbow, shoulder, forearm, etc. I find it difficult to achieve precision.
When I use a moveable extended grip, the extra-fine control from the finger muscles makes the whole thing feel more articulate and controllable.
For me, it’s not a byproduct of other movements, it’s conscious and very helpful. I can’t DBX without it, but I use it even for single-escape and strumming. It makes the movements easier (less pick snag) and more accurate.
I don’t know if my experience is widespread or not.