I tend to view "visualization" mostly as "on-screen memory" - it is a
way
to avoid the user having to *actually* remember the state of (potentially)
thousands of different controls, by presenting them to him/her in a
relatively fast-lookup sort of way. did i solo that? what was the gain
level of that ? what processing am i doing with that signal? etc. etc.
there is nothing inherent to the task of recording and editing music that
requires a visual presentation, but doing without one when working with
anything but the simplest possible setup requires the user to constantly
remember a large amount of stuff - not always easy to do.
mixing consoles, besides actually doing signal processing, also serve this
purpose even though they do not (generally) provide any visualization of
waveform data or present a timeline.