I think the amps-left-on thing is partly a holdover from vacuum-tube days of early studio work (before the invention of the transistor), when it made sense to leave them on because it takes tube electronics a while to heat up and stabilize.

Now, it only makes sense in professional studio applications where the solid-state gear will be used more or less constantly all day (and night), to reduce all those turn-on transients that would otherwise occur.

Alan

Alan Lofft,
Axiom Resident Expert (Retired)