Only time I've ever blown ballast was when I was on the verge of being wrecked at the end of a battle. Had managed to take out all the bad guys, but had taken a bunch of damage in the process and then took one final hit from a helo-launched torp that put me over the edge and caused enough flooding that I couldn't get back up before the pressure overwhelmed my pumps and I went to the bottom. Sat there for a while until the Helo bugged out and all was clear, blew my tanks and crossed my fingers. Fortunately it was enough.
As has been pointed out though.. it's an emergency procedure. You should probably expect some discomfort
