But if you forget to put in the opening of closing brace, you can end up with a totally ridiculous block structure and not notice. Lining up braces means you can check them by eye.
Of course you're never going to notice - after all a compiler for a C-like language is not going to fail mid-way through one is can't make sense of those mismatched braces.
The reason for a brace at end of lien is a simple one - it saves space, either on screen or on the page. I've lost count of the times where a C listing has shrunk by several pages when K&R style is adopted. That isn't just about saving paper, it means you can see more of your code at once. For people who actually read and review their code that's a very definite plus.
But then again, it seems most open-source projects these days are to all intents and purposes write-only. Emacs in particular has a seemingly infinite number of instances where a new variable is declared that exactly duplicates what is being done by another declared a few lines above.