Wealth that isn't being spent is effectively inert and frozen. It may have some precautionary value for the person who's holding it, but this is immaterial once you get to the million-dollar range, let alone the billions. The only interesting thing to ask about is what happens once the wealth is in fact being spent. (Of course, this wealth is generally invested in productive ventures and not literally 'frozen'; but this is a happy side effect, not something that's expressly chosen by whoever holds it. They're simply allocating it so that it 'compounds' effectively.)