Heh, that wasn't entirely intentional...obviously :P

Yup it's mostly Kata based. However our sensei do get us to practice Kendo Katas with the bokuto to get a sense of distance, which is very useful to make our Katas "believable". Self practice works if you're still learning the steps, but is quite hard to develop the metsuke or zanshin required without external observation. Like my sempai said, it's pretty obvious if you're not taking it seriously or lack training as you'll just be dancing with a sword.

There are paired Katas as well, but that's pretty advanced stuff called koryu where it becomes more practical(for 15th century Japan at least) using shinken so mistakes can be a danger.

Myself, I got into Iai to discipline my mind, and to focus.