Also, keep on mind that Git is the engine with which Continuous Integration is made. CI is developers integrating with the work of one another on a regular basis. If the product changed since you started working on your new brach, then your branch is stale and you need to integrate with the recent changes. Why wait until you're done to find out that your branch can't be merged anymore and you have to make a ton of changes when you can keep on top of things at regular intervals and make the final merge as easy as possible, not just for you, but for the code reviewers, the QA guys, the DevOps guys, everyone.