The Meaning of Life, the Universe, and Everything.
The auto jump is cool it really help prevent the button getting worn down by constantly pressing a button over and over again. But when it comes to wanting to swim underwater this feature won't let your character move around underwater without having to swim up to the surface whenever we move. I know I could go into the setting and turn it off. But it would be more convenient to press a button to turn the auto jump on and off rather than to go into settings every single time we need to go into the water.
That certainly would make it easier to use. I normally play with it off because its inconvenient sometimes when your crouched and placing blocks on edges (causing you to jump off and fall), but theres been several times I switched it on. I find myself doing the same thing a lot for classic/console crafting.