How often do you bake? Again, it really isn't a matter of if it will happen but when it will happen. A cookie tray, because it's thin, has a large surface area and small, thin edges that don't provide structure will warp after only a few times. A pie pan on the other hand, may take dozens of times before it starts to warp. Yes, it is still made of relatively thin metal but it has a much smaller surface area, and its sides provide significant structural support. A sauté pan may last a few hundred times before warping, but it too will eventually warp. Just ask anyone in the business how easy it is to find a completely level sheet pan or sauté pan in their kitchen. Unless they have one heck of a budget most cooks and chefs will tell you that the majority of their pans are warped to some degree.