Parkerizing is basically a porous, fairly soft sponge grown on/into/out of the surface of the metal. Fill it with oil and it becomes an excellent grease-like substance that stays put. Would make it a heck of a good finish for steel firearms - someone should try that...
When I thought about getting a Hi Power, I also thought quite a bit about polishing the shoe of the disconnect mechanism, as well as polishing the mags where it rubs against them.
Polished mags make the trigger feel gritty. Parkerized makes it slick. For some reason.