Without this theory, science assumes no such thing, and ultimately ends up with a very difficult problem of defining where consciousness begins and where it ends.
Existence of consciousness is obvious and intuitive to most people, it is rarely disputed (and such disputes yield no useful conclusions or thoughts when they take place), but if the starting point is that "some humans have consciousness, or a potential of a consciousness, and the rest of the world does not", then the problem of defining it seems very hard. Drawing a hard border between consciousness and dead matter seems hard to do while still being completely intellectually honest.
If however, we just assume (as the perennial philosophy does) that consciousness (or at least potential of) is a self-evident property of reality and everything in it, we can view the problem of defining it as more of a question of where in the world is there "more" of this consciousness, where is it more concentrated, where did the potential of it most prominently manifest itself (places like human brains that host it or possibly similarly built computers in the future), and where is it "less" of it (like in a rock formation), then we can use this framework to more easily navigate this landscape.