Keep your application settings in sync (OS X/Linux)

This is pretty cool. For a while I've used a dotfiles repo with various settings and config files in there, but I never got around to writing a script to automate symlinking things on new machines (and which things not to bother with - eg Sublime Text preferences on some remote machines).

Can you explain how sync differs if you use Git as your sync arrangement vs Dropbox? I know that Dropbox will propagate changes automatically, but git shouldn't, so would I have to go in and commit/push/pull changes if I opted for git, or does this make a decision about when to make these changes?