In the rain, it makes a big difference. This Vette blocked me in today, when I finally got around him, went by spinning in third (in the rain). Without TCS, could have got interesting. He wasn't racing, he just speeded up when I was coming up behind him, then slowed down when he got beside a REALLY slow car, just to piss me off. Stupid Vette owners, I still passed him. Anyway, I digress...
Rain or shine, works good, just turn it off if I want to hotdog.