I usually use salt to clean my cast iron skillet, but this morning I was about to pour my coffee grounds into the garden when I realized I could use them to clean my skillet. Just pour used grounds onto skillet with a bit of water, scrub, and rinse. (I pour the remnants outside.) My overly thrifty mind was thrilled to save the few cents I would have used in salt! And yes, coffee grounds work great!
Coffee grounds would be less abrasive than salt. So using them would help preserve that much sought after patina we call 'seasoned'.
When we get our pans seasoned to the point a fried egg will slide around in the pan (with little or no grease) as if the pan were Teflon coated we don't want salt abrading that season away.
Smart thinking, Miz Toosa!