I've always wondered about planetary debris, big chunks of matter make the explosion look more substantial, but I've always shied away from it as an effect as for continent sized chunks to fling outwards impressively like that means that they would be travelling at like 20,000km per second or faster.
I wonder what a planet would *really* look like if exploded? It would probably look really fake
Anyway it isn't meant to be a physics simulation, it looks impressive and that is what matters in a 'fantasy' movie like Star Wars.