What is master ALT?

I’m trying to figure out what MASTER ALT does in the C172 and Xcub. It doesn’t seem to do anything. Can anyone help?

Controls the alternator

What is that?

It is a voltage control unit I think

But what exactly does it do in the aircraft? I want the big picture.

It controls the system voltage.

And what does that do?

It makes sure the voltage in the aircraft stays normal.

It makes sure the required voltage is met to meet certain requirements of the aircraft such as fuel pump etc.