Bypass All Effect Plug-ins
Bypassing plug-ins is a tedious and difficult process. In earlier versions of Logic you would accomplish this by clicking and dragging in the mixer window. Very error prone, and you lose “state”.
The new way — using this command — turns off all of the plug-ins that are on, and remembers the state. The command is a toggle. First time it is issued plug-ins are turned off. Next time it is issued plug-ins are turned back on.
This only affects channels that are selected.
The next enhancement (please) would be to gain match the output of the channel. Level is the same with plug-ins engaged and when they are off. Fair comparison. This would preclude using a Gain plug-in to increase the levels.
Add, remove, move, and copy plug-ins in Logic Pro — Apple Support
If you want to deactivate a plug-in, but don’t want to remove it from the channel strip, you can bypass it. Bypassed plug-ins don’t drain system resources.