So the ISO will change to adjust the exposure, even in manual?Until the advent of Auto ISO I shot Av. Now w/ Auto ISO I shot manual w/ Auto ISO. Basically from the exposure triangle you have 3 factors you can adjust: shutter speed, aperture and ISO. I think shutter speed and aperture are the two main ones I like to control so I let ISO float. If I don't like the ISO value, I adjust one of the other two.
All to personal taste. How much salt to add to the stew - to personal taste