Instead of being stereo amps, a monoblock only amplifies one channel. That is, you need two of them in order to drive a stereo pair of speakers. While this may seem like taking the concept of separates to an absurd limit, there are benefits to be had in terms of stereo separation - hard for one channel to affect another when they are in different boxes. But the most significant benefit comes from being able to locate each amp close to the speaker it is driving. This means shorter speaker cables which is a very good thing. It does however mean another amp stand, another power cable, issues over lengths of interconnects required, wife acceptance factor etc. I also suspect there is an element of "cool" to it - the graduation to monoblocks signalling the entering of high-end arcana.
