I play one-city-challenge a lot, so I'm kind of forced into razing a lot of the time. Even when I'm in a normal game, I dislike managing a whole lot of cities, so I generally employ one of the following strategies:
1 - Form an alliance with someone (or summon Basium) and give all conquered cities to them. The AI gets all the hassle of managing and defending a bunch of cities, while I get to go back to making war. As an added bonus, this seriously beefs up my ally for future wars.
2 - Quite often I end up destroying nearly all of an opposing army before I start actually taking cities, which is what makes this strategy work. I keep all the cities (unless there's a holy city that needs to be dealt with) but don't defend them, and allow barbarians to creep in behind my lines. So when the battle is done, my opponent is either removed or severely weakened, and anyone else will have a lot of trouble moving in to the vacant space. I've also occasionally pulled this off with just Shadows without actually declaring war.