For example, to get a submerged, unresponsive diver to the surface, you might decide to ditch some of his weight.
Huh?
Unless diver is SEVERELY over-weighted this should be avoided. You will jettison diver to the surface quickly.
We were told to make sure you control ascent so you sometimes decrease buoyancy (get air out) and control ascent on your own (own BC inflation/deflation).