The purpose of those "condom" things (actually called a car bra, right, as in brassier) is to allow sand, salt, road grime, and moisture to accumulate underneath them in the winter months. Then, the bra gently massages this nasty stuff against your paint as it shifts slightly in the wind and from vibration. This causes your paint job to deteriorate at an accelerated rate. Then you have an excuse to have the car painted another color sooner.
;)