An experienced club DJ realizes that the venue they perform at makes more money off the sales at the bar than they do charging people an entry fee at the door. As a result, they create an 'ebb and flow' of people on the dance floor. Pushing good tracks to encourage people to come out and dance, and then slowing the pace to give people both a chance to rest and to order refreshments. This back and forth from the bar to the floor is key to the profitability of a nightclub. At the end of the day, the venue is a business. That being said, I'm sure the application of music is different for other jobs, such as a wedding or birthday party.
