Live sand has good bacteria on it, and some helpful detritivores, but doesn't really have cool sponges and other rock-clinging life. It doesn't tend to bring in pods, either. The worms are nice, but worms and bacteria are all you tend to get, maybe a few tiny snails. And that's if you buy live sand that someone got out of the ocean- if you get the "live sand" that comes in a bag off the store shelf, it might have some bacteria, but there won't be much else. It also doesn't have the benefit of providing you with rock that's already too covered in algae for pest algae to have an easy time of taking over.
Live sand and dry rock is better than dry sand and dry rock, but live rock is better than live sand. Both is great.
Live sand and dry rock is better than dry sand and dry rock, but live rock is better than live sand. Both is great.