There was something called a slerp that allowed you to get an object to rotate from on orientation to another, similar to a linear interpolation.
This was fine for some things. but if you wanted something to rotate but only in a certain way it was annoying as sometimes it would get from A to B, but go through Z during its rotation.
IMHO I think for me they're interesting because it felt like mathematically they straddle the line of being nearly impossible for me.
I could just barely do them and felt very accomplished when I could. Anything else was either impossible or easy by comparison.
assuming my maths skills are average here then most people have similar experiences with them.