Is it just me or it looks crazy that the Space Cadet keyboard has thumbs up and down? https://deskthority.net/wiki/File:Space-cadet_guts.jpg
Looking at the keys below maybe it was for up/down.
Looking at the keys below maybe it was for up/down.
That way you can press Control or Alt/Meta (or both at the same time) with the thumb of either hand without a lot of movement. C-f and C-b can be done with either left hand only, or left hand for f/b and right thumb on Control (what used to be Alt, on PC keyboards). Rebinding Caps Lock to Backspace also saves a lot of hand movement. Only a handful of small changes and you get a much better keyboard layout.