It isn’t necessary to know what’s going on under the covers of git. This map isn’t showing under the covers either; it’s just diagramming the shape of a repo.

It is, however, necessary to have a mental model of what your source control system actually does above the covers, and how to use it. It is important to know that you have a staging area and a local repo and a remote/upstream repo. It is important to know that each commit has a parent commit (or occasionally two or more parents). It’s important to know where your commits go, how to put them there, and how to get them back later.

This is barely "under the covers". It really just pictures the core ideas behind decentralized version control systems such as git. You can't reason about decentralized version control without many of these core ideas.

A lot of things aren’t necessary.