Prior to SteamVR input 2.0 you'd use the grip buttons to pose Physbones on Vive. Now, it's part of the trigger and activated upon a full pull. When posing is triggered, you drop the physbone, and it's posed. (if it has that enabled) When I squeeze the trigger I expect to be more confident about holding onto something, not drop it.
An control other than the trigger we use to hold is necessary to pose, which grip fits for on the Vive. A binding for
Physbone pose
may be needed to facilitate this.