I like to imagine it this way: say two people are playing a competitive game against one another. If both players can play the game using their posting key encryption, that data doesn't even need to go on chain. All of of sudden, now it doesn't even matter that Steem has a 3 second block limit. Both players can post actions as fast as the latency of the node they are playing on, just like a normal centralized game.
However, due to the private key encryption, the node running the game doesn't have to worry about things like security. If someone cheats at the game the opposing player can prove it using the rules of consensus of whatever game they are playing. No one would be able to counterfeit gameplay because that gameplay is secured locally on said user's machine.
We are going to see some crazy applications over the next ten years that blow everyone's mind. I guarantee it.