tl;dr; Install the module, set the config value to match your environment, have a stylised login screen and header bar per environment.
Have you ever sat there working on some task and then suddenly someone asks you to take a look at an issue on the Production environment? So you log onto that server, resolve the issue, get distracted for a few minutes by cat videos and then get back to what you were doing. But you suddenly realise that those changes you were just making was not on your local environment, you still had the Production site open in your browser tab! Oh noes!
The problem is that all the environments all looks exactly the same… the only difference being that teeny tiny URL bar, the URL in which probably also looks very similar apart from some environment prefix.