It's called "gain staging" and the ideal is to have both the instrument preamp, the trim and the master volumne set within about 25-30% of eachother. As you get to peak output from any given amplifier (or preamp) you start to pick up the inherent noise of that given amplifier. So the idea is to get that stage above the noise floor and safely within the relatively quiet "headroom" of that stage.

If, at any point, you find a real diversion from the ideal, you may have a poorly designed piece of apparatus in that "stage" of the "chain" and you may be forced to compromise to overcome the weakness. With the overlap that each stage gives you, it is often possible to do this, but two poor performing pieces of equipement can take you beyond recovery. Thus, several "magic boxes" or processors may cause you more problems than they are worth.