CHR stations do it to make the music sound "hotter". Usually at 3%. It's not a matter of getting another spot in. They just drop the last song in the hour if they are running late, leaving plenty of room for spots. Some music sounds good pitched up, Rhythmic especially. The problem is CHR stations play some slow pop songs where the difference is noticeable.
A few years ago I recall hearing one of the weekend countdown shows being over pitched for weeks. Casey Kasem or something like that. It turns out they were dubbing the show into the automation system using CD Players that were pitched. Not only were you getting the 3% pitch from the CD players, but another 3% the automation system was set to when it played back. You can imagine what some of the Mariah Carey and Celine Dion songs sounded like.
Plenty of talk stations speed up their programming too. They get an extra minute or two per hour of spots by compressing syndicated shows. WGY has done that for years. If a show starts at 12:00, they play it back recorded and sped up at 12:01 until it reaches the live feed again within half an hour. Pitch isn't affected though, so no changes in voice. The more pauses and gaps in the talk, the faster it catches up. It starts all over again in the second half of the hour.