Shopify development is a fast paced role. You can easily work on a dozen sites in a matter of hours. All of the tweaks, big and small, can sometimes be hard to keep track of. It's useful to utilize a resource like GIT for tracking updates.
This is the goal of GIT, or version control, a system for tracking versions of code. Integrating this into your Shopify workflow might seem daunting. Thankfully, Shopify dev, Tiffany Tse has a great video on how to get set up.