Looking at a C2S with these. What is the purpose?

Thanks,
Mike

 

The 5mm shims are mostly cosmetic. In theory, widening the track will enhance handling but the modest offset of the ones you cite will not be noticeable at all. OTOH, they do add a subtle amount of visual improvement in moving the tires out near the fender edge.
A number of people use larger wheel shims (from memory) about 7mm front, and 15mm in the rear.
FWIW, I have the 5mm ones, but I'm conservative and was worried about the tires rubbing the fenders when I lowered the car.
But nothing wrong with buying a car that has the shims. And the 5mm ones are likely a Porsche-made part with wheel bolts that include one security bolt per wheel.

 

7mm is most common. i have a set that i'm not using. like the 15mm rears