I built a system to deploy to our test servers that uses a git repository on the test server, clones the repo into a named folder, and checks out a specific branch. QA is able to use a webpage to select a branch, which is automatically checked out in its own folder and a subdomain or cookie is used to do isolated testing of that branch.

So for us, git is an important part of our deployment process, though there's more that goes on especially for production deployments.