Git allows working from more than one system at once without requiring a constant server connection. When I'm on the go and want to make changes to my code from my laptop, I can make commits, I've got access to the full history, etc. All that's required is a pull from my desktop before I leave my office, and I've got a shell script that pulls the repositories for all my projects at once.
With something like SVN, this kind of thing was a major pain, as I'd either have to work just with my local copy on the laptop (leading to poorly tracked mega-commits), or copy the whole file system structure of the repository to the laptop, which quickly gets you into desynchronised territory. Add another developer and you're instantly dead with that kind of system.