@b0rk For me, CTRL-U is "oops I messed up typing my password let me try again". Where CTRL-K is "kill from cursor to end of line", CTRL-U is "kill entire line".
This is really useful for password entry fields where you don't get stars or any other indication you've typed anything, so you don't know where your cursor is.
But, with anything involving shells or terminals, it's complicated. Apparently BASH and some other things think CTRL-U is "kill from cursor to beginning of line" and many other shells including ZSH think it's "kill entire line". I don't actually know what interpretation is in charge in a password entry field... but I still mash CTRL-U when I know I mistyped something.