When youre in Manual mode you select one input, and then automatically adjust the other to zero the Exposure Indicator. Then you direct the camera to a new gray by over or under exposing, based on your assessment of the scene.
Please explain how that is any different than what you described. As I said before...using an auto mode is no easier than using Manual. You still need to learn how to compensate for exposure. The big difference is that compensation is treated separately...it doesnt get lumped into the process of setting exposure. This fact makes it easier to understand.
Here you have a function whose singular purpose is to adjust for differences in illuminance. Well, that kinda forces you to understand why scenes vary in illuminance in the first place.
We all know there are many different combinations to achieve a "proper" exposure, but generally there is really only one combination for the creative exposure (the ideal shot). When shooting in manual mode, the process is fast and deliberate, you use your knowledge of aperture, ISO, and shutter speeds with the conditions present, and make your adjustments.
You know your limitations when hand holding (
shutter), you know your sensors acceptable ISO ranges (for noise), and you should have an idea of what aperture you want for the given shot. Part of the learning with manual mode is how all these come together and on top of that how you can manipulate all these to get the best creative shot at any given scene.
Yes most people will read the light meter and adjust their shutter to a balance, and then from there decide if that is an acceptable exposure. If not a simple flick on one of the dials takes you to a new exposure.
Some photographers demand consistency, and manual mode is an awesome way to ensure your shots are consistent from frame to frame. Whether it's for something like consistent, swift editing in LR, or for a Pano stitch with varying lighting conditions or shades.
Using manual mode when you don't understand how the settings all come together, isn't going to benefit a new recruit. The process of reading, learning, trial/error, and putting those ingredients together to create a desireable end result, strengthens a new photographers skills and understanding of what's going on with their camera/photos. Therefore it is a useful tool in learning about photography.
I shoot Aperture Priority and Manual, with any other mode filling in less then 1% of the residual time, in case it appears as though I don't believe in Semi-Automatic modes.