Years ago I bought a very nice pair of repro step plates for my 1929 Chevy. I couldn't decide if I wanted to drill 4 small holes in each of the good original running boards
, but after 6 months or more I finally mounted them.
Sure do wish I hadn't done that!
To answer your question, they do save some rubber mat wear, and some step plates, like on my 1927 Dodge, have a raised shoe scraper edge to remove mud before climbing into the car.