It's like car racing as opposed to foot-racing. Normal chess would be like running, and people compete about how fast they move their legs. Correspondence chess is being given a car, and learning how to drive, change the gears, and take the curves so you come up on top when you reach the goal.
The extraordinary thing about this is that you and your opponent take turns building the racing track, like creating a series of chess puzzles for each other, and if you manage to build a ravine you have to jump through to land on the other side, but your opponent falls into the pit, you win.
Chess engines have become so good that it seems the gap between slow hardware and fast hardware has been abridged, and one is able to creatively lead the game into any kind of positions one wishes, because the draw path is very wide, and it allows to many playable moves to be best.
You might want to try it one day, as I haven't found any better game than this. Had I found it, I'd be playing it instead of analyzing my corr games and hanging around these forums, but there's nothing else quite like it.