Yes, it's a menace to laning.
No, let the rage over missing health bars continue.
I can think of no situation in game where I would want to remove the health bars. It's useful for those making movies with the engine, but not during the game itself. Since it is nothing but a hindrance in game play, there should not be a default bind for it. Alternatively, make the option 'Always display health bars' do what it claims to do and override the display info key.
Well... I thought it was annoying when I didn't know what was doing it, since I couldn't find it in the key bindings. But upon realizing it, when pressed you can simply press it again quickly and they come back.
I can provide a reason. Note that I always keep them on anyway.
When creeps are close to eachother, their healthbars overlap making it sometimes impossible to see the last shred of life on a creep you're trying to lasthit. Toggling the bars off and simply hovering over the creep you want quickly solves the issue.
I used this was super annoying until I figured out that you can just press (') to redisplay them. This isn't needed, trust me.