I enjoy shooting M when lighting is tricky for the camera and I know the "look" I want. I'm no pro though, but when I shoot events outside with people (or just shoot people), lighting is more or less consistent. I have my exposure set so peoples skin looks properly exposed, not worrying about the sky and whatnot for most shots.
Sometimes I establish a second exposure for shooting in the shade and that mostly consists of flicking the shutter dial. Works for me since in post everything is so even from pictures to picture. Allows me to quickly make basic adjustments and then focus of a couple pictures that might need some attention, cause there are always a few. Keeps a set of photos "consistent" at final output too.
Rig shots require manual exposure too. Other than those two situations, I enjoy just shooting in Av around family and friends for fun to just capture moments of happiness and interaction and still retain some ability to be creative with DOF.
Shooting M is an acquired taste for most. I'd say those who need to shoot M figure it out eventually because it's truly useful while shooting and afterwards in post. Some never need to shoot M, because like me sometimes, it's nice to use the dslr and it's brains when it isn't super important to streamline edit time and you can just focus on whats going on around you when lighting changes too much (like inside room to room to outside to shade etc)