What breaks if I delete the folders named Public and Sites? The default home folder on Mac OS X has folders named Public and Sites.

I never use them, so what will possibly break if I delete them?
As an alternative to deleting them, you could consider hiding them in the Finder instead. To do this, launch Terminal then enter this command:

chflags hidden ~/Public ~/Sites


If you ever want to make them visible again, you would use this command:

chflags nohidden ~/Public ~/Sites