You might try posting on the Expert Forum dealing with Reconstructive Surgery. Regards ....
A plastic surgeon told me that the muscle is not widely used. He said that if you put both arms straight out to the side of the body and make tiny circular motions, that is when you would feel that muscle, or lack thereof.
However, I've had women tell me that it causes them issues when swimming.
Not sure if that helps you or not. I chose DIEP reconstruction which is a tissue transfer that doesn't move or bother the muscle.
Another one said they are on a rowing team and that sport specifically uses that muscle.
fyi .. in case you decide to start rowing :)