Well, I am not a pro guy of course , I don´t try to stand this as the way it has to be or similar. It´s just I find it useful in my searching of 60s sound.
The VU meter is simple and I try to have it moving around 0 and a little in red part, avoiding danger red light which means 0 digital, although most of times is not so noticeable as I can find, I try to listen by ear paying attention to zones where red light is and trying to verify if it sounds really bad. Sometimes it sounds clipping and it´s ugly so I go down with level but sometimes it doesn´t sound in a bad way. Anyway I force myself to avoid red by leveling a little lower instead using a brickwall.
The main problem I think is that a track which turns on light red but doesnt sound ugly can create an ugly sound in the future by passing these red peaks through another instances and then they become ugly.
I don´t know if this can have sense, it´s too late here...
Mac Pro 5,1 / 6-core Intel Xeon / 16 GB Ram / El Capitan / Reaper / H******* Mixbuss