I've had this question on my mind for quite a while and looking at the web, I couldn't find an answer to this question.
I've had a lot of physics experiments involving springs, unintentionally dismantled a hair clipper once, helped my dad repair his car, and all of them have very identical springs.
Here's an image of a variety of springs that are used for multiple purposes:
So, what's with the spiral/helical shape? And why are they "curled" in circle-like shapes. Why not triangle, square or any other geometric shape? What exactly is the physics behind this.