As mentioned, depending on several variables, the benefits can be from minimal to obvious! With the right synthetics, engine wear can be reduced and operating temps can be lowered also in addition to freeing up some HP. All synthetics are not created equal either. Personally, I've used Amsoil for years in my personal, tow and race vehicles and have seen all of those benefits. Oil, trans fluid, gear lube and wheel grease.

Amsoil source and info site.