Ive been pondering what the real purpose of it is, and I cant seem to find a consistant answer that makes sence. Mine is ugly and has dirty spots on it, and I take my car to alot of car shows, and its alittle embarasing to show off the stock LT1 with some crappy looking thing on the hood...
Ive heard this :
#1- It keeps the heat in from cooking the paint off the hood of your car
#2- Its a fire blanket, and if your engine starts a fire, the plastic tabs melt and the blanket puts it out
#3 - Its just a sound deadner
Just to be the devils advocate, for #1; Ive seen people with aftermarket hoods that do not retain the sheet, and their paint is still prestine. For #2 Are the manufacturers really that smart?

Only one I can agree with is #3.