Why Exposure Compensation in Manual?

For a few months I have been shooting in M, Manual, usually action, birds. I want to control the DOF and freeze motion. Since the light may be changing I use auto ISO.

So I've wondered what's the use of my exposure compensation, (+/- ) button. So i assigned it to do another function.

Wow, a wrong choice. I follow Robin Wong to learn things about my Oly. Spoiler, basically I now use exposure compensation when in manual made with auto ISO. View this video to know why,