Parameters are more expensive becouse it precalculate all variation you can make with changing this parameter. But this cost is only on compiling time so before the game is start, is like construction script in blueprint.
At the end better use parameters to make master materials. The time is take to compile shaders is only on loading time but on runtime of the game is changing nothing between a costant and a parameter. The unique difference was that you can use parameters via blueprints to make a caind of customizzation and costants not allow it.