A single place for setting fairly basic values (UIRoot) is in itself a good reduction of error potential. Generally, I would load things dynamically instead of having everything loaded from the start though, but that's not necessarily needed depending on the complexity of the menu. It's a classic DRY issue - if you need to change your root values now, you're in for a headache. You'll also have to check each and every root in your project to make sure they're all the same, because otherwise none of the pixel values will correspond properly to each other. So there's repeated overhead in your setup, with no real added value other than 1 level of hierarchy saved for organization.
I see no compelling reason for it, based on what I see here, and honestly if you were one of the programmers on my team I would bonk you on the head with a paper and make you change it.
If you have significant changes, then you can potentially justify it; say an entirely different camera set up, or something like that. Right now, it seems to just be for saving 10 pixels on the x-axis in the hierarchy view, which seems to be a big headache for not very much gain.
Assuming that all the roots are identical anyway, then changing it is nothing more than dragging the content into your "main" root and cutting out all the other stuff.
