I've known some people who have used these in the past, few of them still do. It seems the biggest reason to use them is if you've got large feet, otherwise they're an added hassle when dealing with your bindings.
Just as it was with skateboarding, risers aren't needed unless something is catching. I put risers on my skateboard when I ran large wheels and kept my trucks nice and loose because the wheels would smack the board, and if I had large dragging ass feet and refused to buy a wide board, I'd get risers. Otherwise I view them as obsolete, but I haven't used them so I can't give an educated statement.