It is more consistent. All of my code is now (in my case) Scheme. This makes it easier to change things as you don't have to go between two different languages. And it is simpler.
My favorite reason is the fact that I can use S-Exps. I no longer have to type the ending tag. I remove the possibility for spelling it wrong, or forgetting the slash. And it takes less space and is easier to get the placement correct, as you just utilize paren matching.
This could be solved by some editor placing arrows showing which tags are parents to your current position, but I don't think that's available (at least not in emacs, sadly), and paren highlighting is.
Also, never missing a closed tag, mispellings, abstractions, etc. All very nice. When loading a broken page in chrome, it's crazy how much the html will be transformed, so that it's hard to tell why the page renders a certain way. A bit easier with this approach.