Similar to the system in-wall speakers, in-ceiling speakers system is the sound of home theater system that is integrated with the walls of your home. The difference, in order to get vibrate delicious, and the results of three-dimensional effect is more real anymore, then you are forced to perforate at least some of your walls for storage in-ceiling speakers system.
Another advantage of in-ceiling speakers system, you are setting up a multi-room music system, and a little extra could be a great surprise for your friends and your girlfriend to feel the sound 'not seen'.