I've got the more primitive TC in my 2000 S, and while it has only gone off a few times on the street (mostly when I try and make a right turn from a stop and I get on it too much...) it comes on virtually *every* *single* *corner* if I am on track and I forget to turn it off first. I will start a hot lap, hit the first corner at speed, and whoops there it is... On the TC, I think it is cutting the fuel and possibly braking one wheel due to inside wheel spin on corner exit. I left it on for the first few years but no turn it off.
Last time out, I had a big spin in the wet and I wonder if leaving it on would have helped me?
If my car had the more advanced PSM I'm not sure if I would leave it on or not. The "fast" folks that I have ridden in that have PSM usually turn it off and there is a lot of reports on the Cayman Register about folks overheating their brake fluid due to the rear brakes activating so much due to PSM. On my Boxster I go through 2-3 sets of front pads for every set of rear pads, and those guys go through 1:1 or even through the backs faster.
With the addition of Sport Mode Software, which supposedly raises the limits before PSM intervenes, I wonder if that makes a difference.
All that said, I leave it on for street driving
But I don't think I would pass on a car that didn't have it, if the rest of the car spoke to me.