Sawtoothing in games was initially a brilliant way to control the amount of a level that had to be loaded at any given time. It allowed clever developers to unload sections of a level they knew you could no longer reach because you couldn't jump that extra foot or they set the stairs on fire.
Nowadays, we use it for a far more lazy reason. The modern RPG tends to fall into this (just a tiny bit deeper than you can jump) trap super often. Complex architecture and beautiful level design and then you pop out the sewer covered in shit and realize the entrance was right next to your house.