When is abstraction to much abstraction

> Been reading about LessCSS, SASS & CoffeeScript and I'm wondering just generally if that is the way to go? When does abstracting, make something simple more complicated. Should you be doing things in the simplest way possible. Is it introducing more possible points of failure?
If you introduce these steps are you also increasing the understanding needed to edit something from just CSS to CSS + SASS?
Perhaps I'm just confused post getting geoffed on Friday.