of course there are exceptions. in general a parasound JC1 monoblock (for example) offers 850 watts at 4-ohms in a 107 lb chassis while the same power in a two channel amp would have prohibitive weight and size. It is a way to support the needs of more demanding power requirements while not requiring a hoist to get it into your room.
I tried dual mono block amps and while a high quality design the overall tone and transparency was not what I was after.
As long as the amp has adequate power and capabilities at lower impedances depending on speakers I prefer the sound based on how they sound and not whether they offer an advantage on paper because they have an extra power supply and power cord.