In my experience, Macs use up a ridiculous amount of "System" storage for no reason that users can't delete. I've grown tired of family members asking me to help them free up storage that I can't even find. That's the major issue from what I've seen; unless this app prevents apple deliberately eating up 50%+ of the storage space of a machine, this doesn't do much for the people I know.
There's no magic around it, macOS just doesn't do a good job explaining it using the built in tools. Just use Daisy Disk or something. It's all there and can be examined.
