I don't personally, but I can see why others would. Take gaming forums, for example: let's say there are four nodes, one for PlayStation/Sony, one for Microsoft/XBOX, one for Nintendo, and another for PC gamers. Having a unique style for each node can help create a visual distinction between each one (like a blue/black/white color scheme for Sony and a green/black/white for Microsoft).
That said, it does require supporting more themes and there will always be users who don't like one or another, so I can see why most wouldn't want to go this route.