Delays: When do you use a stereo delay and mute one channel? When you use ping-pong delay?

[mementus]

Hello

I am interested in these 2 scenarios. Let's consider a Modern Pop Rock enviroment, please.

The first:
When do you put a stereo delay, hard pan an instrument let's say to left, mute left delay channel and tweak the right(panned to hard right, I suppose)?

The second:
When do you use a full ping-pong delay?

Glad to hear!