Version controller system provides the flexibility to properly maintain code, changes, and versions of the application. Using VCS, a complete team can work together on an application, and they can pull other team members' changes and their own changes to the system without any big troubles. In case of a disaster, VCS provides the ability to fall back to an old, more stable version of the application.
Oh wait! Are we talking about VCS? Did we mention Git? Nope! So, let's start with Git.
Git is a powerful tool. It monitors changes in each file in a branch, and when pushed to a remote branch, only the changed files are uploaded. Git keeps a history of the file changes and provides you with the ability to compare the changed files.
Note
A very informative and good book on Git is Git Essentials published by Packt Publishing. Also, an official and free book about Git can be found at https://git-scm.com/book/en/v2.