My best understanding, at least with the roots, is that each endpoint is essentially a "water collection zone". So long roots with minimal spread have fewer intake points for the water, whereas shorter roots that split often have more intake points and therefore let you get more water.
I'm assuming that sunlight is related more to the number of leaves you have on your branches, and I've noticed that the longer the branch the fewer the leaves on it. Therefore similarly, you get more sunlight by having many splits in your branches to maximize the number of leaves.
Note: This is all observational, I have no proof that my hypotheses are correct, but they seem to work decently for me