Page "Theory of everything" Paragraph 54

A motive for seeking a ToE, apart from the pure intellectual satisfaction of completing a centuries-long quest, is that all prior examples of unification have predicted new phenomena, some of which ( e. g., electrical generators ) have proved of great practical importance.

And like in these prior examples of unification, the ToE would probably allow us to confidently define the domain of validity and residual error of low-energy approximations to the full theory.