> thumbs are each responsible for 0.5 keys Depends on the person and setup. There's both thumbs for space, that's true. But then you have a thumb each on left

> thumbs are each responsible for 0.5 keys Depends on the person and setup. There's both thumbs for space, that's true. But then you have a thumb each on left alt and right alt, and they're not redundant because alt is usually pressed in combo with another key so you use both. Then you've also got the windows key, which is one thumb only, and also the printscreen key, or whatever key is in the same position on the other side of the board, for the other thumb.