When people tell you they use manual mode, they are not simply centering the needle for each shot. Doing so is silly, it's just a slow version of Av or Tv.
Using manual exposure generally involves getting to the desired exposure some way (this can be using the meter and the histogram, using an incident meter, using a rule of thumb....whatever). The point is that once you have reached that exposure decision, M mode keeps that setting for you. This is the attraction of M mode.
I understand that.
I'm just pointing out the foolishness of using M mode in a way in place of one of the automatic modes which will do the same thing.