Not sure if there is already a way to do this (without manually muting each channel).
I have a solution open just now with 16 channels. My CPU usage is pretty high (getting some crackling) and I wanna track down with VST(s) is causing me the grief.
Normally, I would have to go through each channel and mute til my CPU drops, so might be nice to have an indicator of what is eating up the CPU (maybe on the mixer strip)