I simply don't have room for a stereo amp in my main system, so monoblocks are a must. They sit behind my speakers, and yes, I've been able to use very short speaker cables. Of course, your interconnects between the preamp and amp will be longer, but if everything is fully balanced, that probably won't matter.
Typically, a stereo amp is going to cost less than the equivalent monoblocks and will take up less space.
For me, the decision had more to do with my available space than any sound quality or performance issues.