I’m a teacher. Regular whiteboard erasers leave marker residue on the board. The residue builds up so fast during class that it makes it hard for my students to see what I’m writing on the board. So, I’ve just started using this cleaner instead of an eraser at all. I have two very large whiteboards, and I end up going through one of these bottles about once a month or so. I hate spending the money, but it saves time and energy so I do it.