Well if you want to reduce unsprung weight, which a lot of track guys want to do, then usually people go with a smaller size wheel because generally speaking having more tire weighs less than having more alloy wheel.
Although, on the last car, we bought the optional 20" wheels actually weighed less than the stock 19's (which were blocky with fewer but much thicker spokes).
@Find Finn I think back in the day, many cars gave a noticeably harsher ride if you went with bigger wheels/thinner tires. However, I would agree with you - in the last few years suspensions have come a long way and you can get great performance, have larger wheels and not have a brutally punishing ride depending on the car/chassis/suspension.
I think a lot of folks will also run 15's and lower the car slightly when they upgrade the suspension. The difference between stock 15 inch wheels and 16's in this case is about 2 lbs per wheel. Not insignificant.
Huh, that's interesting!