Provided that you aren't pressing so hard with your pencils that you're damaging the paper, this eraser will cleanly remove up to 4b lead. Unlike a lot of plastic erasers, it doesn't fade ink when cleaning up sketches. I like to cut these into triangles, because they'll withstand being razor sharp, which is great for highlights and tight spaces.
Perhaps my only complaint is that they are a little messy, but no more than plastic or rubber erasers. Foam erasers are a must have for my illustration needs.