[LAU] Sound newbie question re: PCM volume control ??

Hi; I have been lurking on this list for a month or so hoping to learn something about sound drivers, alsa, etc. But I do have a question that is mystifying me. Why is there a volume control for PCM? Isn't PCM an on/off thing? Either you need to sample a stream or you don't? Shouldn't alsa code just use PCM as needed without user intervention? Is there real instances where users need easy access to PCM settings? All my playback devices have their own volume control; usually two or three controls i.e. software volume control in alsamixer, an application volume control and often a physical control on the hardware. Computer generated sound is complex enough without throwing in unexpected extra volume controls. A secondary question for experienced sound users: How, or in what order or priority, do you usually the adjust volume levels of alsa, application and physical (knob or button on speakers etc.) controls? So far I just have been twiddleing a little of this or more of that with no real rationale. -- Regards Bill Fedora 11, Gnome 2.26.3 Evo.2.26.3, Emacs 23.1.1