Compact frames take the standover height part of bike fit out of the picture. It means that you, the guy looking for the right bike fit, can choose a bike frame based on reach (the more important dimension) and not your inseam. This is especially good for people who have a long upper body and short legs. Some claim that compact frames are stiffer and lighter because the frame tubes are shorter, but I don't know if it would be enough to really notice. The nay-sayers to compact frames complain about the non-traditional look. They also say that the only reason bike companies make compact frames is to make fewer frame sizes. While some companies have reduced the amount of sizes available, many still offer frame sizes in the traditional 2cm increments.