I don't know if they always necessarily sum the program, but 9 times out of 10, the listener is only going to hear one channel or the other. No one is going to hear a stereo image when there is speakers placed all over the club!

Keep em in the center

Tim

The other reason to mono dance music is because of the " center buildup". It will generally give you a 6 DB increase in the bass and bass drum sound, along with anything else in the Mono Center image of the mix. Obvious advantages for orgiastic oriented dance music. And in good clubs with good sound systems, I have enjoyed the stereo sound. It is perceptible but yes, generally not probable.

Push, push, in the bush.
Ms. Remy Ann David

This is fine for dance music, extremely annoying when I walk into a club to mix it and they tell me the system is in mono and everything is subgrouped for my ease... nothing more annoying...