HEARD of them, never used them.
As you are probably aware, the human eye can't see very well through an f/16 lens opening, especially in the dark. You compose the pic with the lens wide open and it automatically stops down when you push the shutter button. It wasn't always automatic. In the early days of SLRs, you would manually open the lens, compose the shot, then manually close it down and finally take the shot.
A "preset" lens was an improvement over full manual. You decide on the exposure first and, of course, the required aperture. You set a mechanical "stop" on the lens so that you can manually close down to the desired aperture without looking at the lens.
The "Honeywell Pentax" Spotmatic (1964) was advertised as the "world's first automatic SLR" because the aperture automatically opened wide for composing and automatically closed down to the (manually configured) shooting aperture when you pressed the shutter button.
That's why I get a laugh out of those that scream "Manual is the only way to go." Hell, most of them don't know what full manual really is. (There was also a time when you had to manually move the mirror out of the way!)