It's only been the past few years that employees at my company started receiving sick days. Before, we would get half pay and then have to portion it out with our vacation days if we didn't want to end up with a short check. This was supposed to keep people from calling in if they weren't really sick. Mostly what it did was make people come into work when they didn't need to be there, resulting in them infecting the entire office with their bug.
We have seven sick leave days a year, but most people don't take anything like that many, unless they catch something really bad, like a bad case of the flu or something. However, we also don't have as many people coming to work and spreading their germs to everyone else. That's the main benefit, in my opinion.