Sending return tracks into other return tracks

Can someone help me explain a bit more detail about the technique behind sending return track into another return track? i.e. a delay into a reverb?

What are some example genres or sounds that this is typically used for?

dub Reggae for a start.

I use it for effects on Drums, may run a reverb into a delay (although many people tell you to never mix the two) and so on…