Let's take the same computer gaming analogy which has helped us to understand the basics of Git.
Think of your favorite game that allows you to save the state of the game in your system at any given point of time and resume it later on. Now let's consider a situation where you are in some remote location with access to a computer and want to resume the game, but are not able to because the saved game file is not accessible from that system.
Apply the same situation to your data files. On average we spend most of our time of the day at two to three different locations; think about how productive it might be to continue our work across systems without having to start from scratch on each new system we lay our hands on.