The cleat covers are really necessary so you don't get stuff like sand, grass, or mud in your cleats (Speedplays). They always go on as soon as I am off of the bike; not because of scratching the cleats, but because it is nasty to try to clip in when dirt gets in there. I once used almost a whole water bottle trying to get sand out of my cleats when stopped at a beach. And then there was the time my husband fell right on his azz as we walked to into the lobby of a hotel on a bike tour in Quebec. It was raining, they were wet, and believe me, he wished he had his cleat covers on.
I lube my cleats every 3-4 weeks and they work like a charm.