My suggestion to use Git was that if you are working on difficult lessons that will require multiple browser sessions to solve, you may want to be saving your work somewhere more reliable than your browser cache. In such a case, being able to revert to earlier versions is also useful. Plus, most campers don’t learn how to use Git until they’re forced to.
I don’t know why you would screenshot your code instead of copying it into a file, but whatever floats your boat.
Since your solution is submitted by running the test, those solutions would also be saved in your browser cache. If you complete a lesson and then immediately go back and do not see your solution, it means that something is preventing FCC from writing to your browser cache (incompatible browser version, security settings, other extensions, etc).
Your solutions to the projects (which are required for certain certificates) are also saved to your public portfolio.