It doesn't serve any useful purpose, but some still believe that it helps keep tension of the springs. The best caps are those with hard rubber primers made of thin metal plated with nickel. For practice I use light alloy ones with spring tensioned brass primers because that is all I could find locally in 16 ga.
Dropping the hammers really does relieve the tension on the main springs, and a spring which is left in a compressed state for an extended period will eventually take a set. But you don't even own any double guns Jagermeister. So tell us... since you don't own even one lousy double shotgun...do your snap caps cycle through your Remington autoloader?
I use several different brands and types of snap caps including the plastic ones, but never had a problem with the rims disintegrating or breaking. Some of them are probably 20-25 years old. I wonder if exposure to some specific bore solvent or oil is what caused the plastic cracking problem that some have experienced? Syracuse Lefevers are another gun that can easily be manually de-cocked, eliminating the need for snap caps or dry firing into a wood block or piece of brass.
