There are different gaskets for different applications, it isn't a one size fits all type of deal.

If you have an aluminum head with a smooth gasket rail and a good valve cover with a smooth rail then the gasket's job is easy. A lot of Mopar big block valve covers are built wrong with the rails in the wrong place. Those valve covers twist the gasket and it is hard to find a gasket that will survive.

It took me a few years of trial and error but I finally figured out how to eliminate valve cover leaks on a big block Mopar. The light bulb came on when I carefully measured the valve covers and the cylinder heads. Once I figured out that the parts didn't match I understood why I always had leaks.