Doing the doors, boot, and cavity can easily add 50+kg to the car, that's going on an estimate of 20 odd sheets of it. So its the weight of an extra female in the car, but then you have the added weight of the passenger as well if you carry one, which all adds up to extra weight in an already heavy sports car. I'm not arguing that the odd sheet on the door's is bad.
It's just extra weight that will probably be disregarded in a few months when folk are looking at exhausts and air filters to scrape a couple bhp back because their cars too slow.
Going by the stats of letstorquebhp.com, the 350z weight is 1525kg, adding 50kg will reduce your bhp/ton from 183bhp to 178bhp.
Small difference sure, but it's not insignificant on a sports car.