It's a useful shortcut - doing it from the command line was a bit of a hassle, particularly when everything else could be done through the web console. For a while I was tweaking a Windows EC2 instance - 'tiny' was enough for the application it was hosting, but if I wanted to install patches or new components it was much more responsive the next size up. So, I'd shut it down, crank it up a step, make all the changes I needed, then switch back down to tiny.
I wondered at the time why they hadn't bothered including a dropdown menu for instance type, like they had with other parameters - hardly a major undertaking, you'd think. Still, they've been rolling in a lot of new features to various AWS services lately, and letting the console lag behind a bit - let's hope the console catches up now.