Who among us can claim never to have thrown a sickie? On a sunny Friday, when we know things are slow at work and there's a garden chair just calling to us, its hard to resist and do the decent thing. There's an argument that if it brings us back to work on Monday with a more positive attitude then it's better for the business.
However, in some organisations sickness absence is endemic. People actually believe they deserve it, and many will take weeks or months off for minor ailments that they could easily work through if they tried. It paralyzes the business and costs the employer (or the taxpayer) a small fortune, and something has to be done.