I do for a different reason. My laptop overheats CONSTANTLY. Right now, it's sitting on top of two giant textbooks with a desk fan next to it, and it's still pretty warm underneath. If it had a raised bottom so that the finicky parts weren't stuck against the table/my lap/whatever it wouldn't heat up as much and I wouldn't have to freeze my fingers off.
Ergonomically I can't tell a difference, and the downside is that raised keyboards tend to make for a bulkier, heavier laptop. Unless you meant like a slanted cooling pad for placing under laptops? Those are a pain to carry but really nice.