Decals will be fine. I put liquid dishwasher detergent in a bucket of water to clean compound out of all my buffing pads and power balls. A quick soak and a few dip and ring outs get them clean as new in a matter of minutes.
One thing not mentioned, I put a bonnet on my PC and use it to apply liquid wax as well. Really saves time and elbow grease.
Also, if you have a black car the PC is the only way to go. My makita has never touched my black cars. It leaves too much swirl behind. I get lots of compliments on how shiny and perfect the paint is on my old black suburban. It is in fact far from perfect but definitely a testament to how well the PC works.