This is a cool feature. You can mark files as “yes, I know this is tracked by Git, but I don’t want my changes committed.”
For example, there’s a config file that’s checked in. You need to make local edits to test with. However, you often accidentally commit those changes (you forget). But you could tell Git to ignore changes in this file. Let’s say we have a file config.php that we want to edit locally and leave edited.