Obviously don't add it if you don't understand it (never trust a random on the internet).
But to answer your question, this:
On any terminal prompt in a git repository, I see username/hostname/path (as normal), but then the git branch (in yellow) followed by some "bit flags". In the picture, the exclamation mark tells me I have modified some file(s), the question mark tells me I've added some file(s). Just after a commit, the bit flags disappear to tell me that the working directory is "clean."
There's other flags, as described in the script. If I'm not in a git repo, I just see the normal terminal.
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