It boxes you in, it raises questions of realism (because it's hard to be convincing), and it requires a degree of profundity, since it's the foundations of the world.
But after some recent reads, I add another point: if you do have to bring in metaphysics, keep at least part of it mysterious. Yes, the Great Hall can be a microcosm on which the universe depends, with the sun the moon and the stars in the rafters. Yes, the hero can need to wind clocks to keep the universe going right. But don't let him understand all of why he does it. Especially not if he's a viewpoint character. We have to understand him, then, and if we can fathom a character who can fathom the universe -- why, it's not a very impressive universe there.
(Letting him reveal himself in dialogue can also be dangerous. Beware of how much a being of metaphysical significance confides in anyone.)