Sometimes Clients insist on audio being louder, especially when you have background music with some VO (Voice Over). However, they have no idea with the audio meters mean and have no concept of what db means or why it's shown as a negative. Let alone trying to tell then why peaking is a bad bad thing.
They just like it all LOUD ENOUGH TO HEAR.
Here's what I do. When I know the audio is correct, the voice is around -6 or so, the music is (depending on the project) -12 or -20ish and they want to hear it LOUDER! I CAN'T HEAR IT! I quietly hold down SHIFT and nudge the Mac's audio up with the Increase Volume Key.
Shift will mute, while held down, the plonk noise of increasing or decreasing the audio.
They think the audio is now louder (I always try to keep my edit bays Mac's audio at at least two below maximum) and you won't have audio that needlessly peaks.
Another fun Audio volume trick is to hold down SHIFT + OPTION while you adjust the volume which lets you adjust the volume in 1/4 increments per visual block. I'm not sure if you can mute it while doing this though.