So Safari stops running out of memory and crashing. (I assume that's at least part of the problem. It's much worse with 64-bit than it was with 32-bit.)

So I can keep 2 websites in RAM at the same time instead of it reloading when I switch between them.

Apple fixing Safari's bad behavior and letting it sleep its state to flash would work too, but 6 iOS versions later it looks like they're incapable of that.

So you can keep more apps in memory without having the OS put them to sleep.