I'd like to be able to symlink content into a shared folder. There are times when I'd like to consolidate items from the various sources into one destination on my backup/secondary. For example I don't want to sync all of my iTunes Media but I'd like to pick and choose items that aren't available from the cloud into a common shared folder. Perhaps it's safe to share each of those folders but the overhead of setting them up is greater... alternatively it may be easier to share a common ancestor folder but that may include gigabytes of files that I don't care to backup.
BTW, I've successfully synched .git repos with Dropbox. Though I did occasionally end up with conflicted copies if I moved between machines too rapidly. Since Git is just a collection of files you'd really only have an issue if you synched between devices with radically different versions of Git installed. I can't speak for how Subversion would handle synchronization.