I think it's probably more if you are not aware of tuning stereo width or stuff like that, it'll get you to a nice "default". But obviously if you're more knowledgable you might tune this yourself.

For loudness there are certain "standards": https://support.spotify.com/us/artists/article/loudness-norm... - it just makes distribution of your music much easier.

There are probably (or soon will be) different presets for mastering a rock track or an EDM track or a jazz track, with different targets for dynamics, loudness etc.