Hard-pan and widen non-essential sounds
Since summing to mono will cause a decrease in volume for hard-panned elements, hard-pan non-essential sounds.1
This can be especially useful for reverbs. Using a stereo widener to reduce the mid channel will sound great in stereo and more or less null in mono.
Notes mentioning this note
Stereo processing
Stereo processing [[Use short delays for stereo width]] [[Creating a fake double track]] [[Use a graphic EQ for stereo widening]]...