I take nutritional supplements because I believe they are beneficial to my health. I know that some people still think they can get all the nutrients they need from their food. The question I would ask these people is "how do you know you are getting enough of everything that your body needs?"
Research has shown that various health benefits can be obtained by taking certain supplements. For instance, a recent study shows that Vitamin D can help reduce the risk of colorectal cancer. Read more about this study here.