The more practical aspect which has yet to be mentioned is that monoblocks can get you the biggest dual-mono power supply (plus heatsinking capacity in traditional solid-state amps, or output transformers in traditional tube amps) without creating one inconveniently large and heavy chassis. Who really wants to contend with a 200lb. amplifier? Of course, you pay for those two chassis instead of one, and need two power cords. But with the new smaller switching-amp designs these issues can be finessed -- you can have a powerful stereo amp with dual-mono supplies without it getting too large or heavy, or you can have separate monoblocks for cable length flexibility without paying for (and needing to place) two full-size chassis. So I think it tends to break down this way: for high-powered tubes, monoblocks are typically the way to go, while lower-powered tubes can work well either way; for traditional solid-state either configuration can work well, with the ultimate high-powered edge going to monoblocks; for switching-amp solid-state, you pick it.
Are monoblocks better than stereo, with tube amps?
I am only in the research phase of audiophilia. My present system includes a creaky NAD 150w amp and ghastly sounding speakers from a "rack system" circa 1988 Stalingrad. Anyway, I am hoping to eventually save for a tube set-up with a kind turntable and sweet, costly speakers. I am wondering if there is any advantage to using a monoblock system for amplification and why.