To me, I think that the space savings is exactly what should be emphasized to beginners. I love functional programming as much as the next person...well maybe almost as much...but quicksort without mutation is not quicksort.

Showing beginners quicksort with mutation pulls back the curtain on functional programming and reveals the wizard. Functional programming, so long as we have Von Neumann machines, is a layer of abstraction and who am I to argue with Abelson and the Sussmans that beginning programmers should be introduced to abstraction layers as quickly as possible?