Even if the value is minimal. We seem, as an industry, to have come to the conclusion that meaningful content offered to the target audience for free is very important to traffic retention. In special cases, it can drive qualified traffic by itself. Contests are a big boost to traffic.
Intelligence is required, however.
You must realize some people will respond to nearly anything for free, but many will be genuinely within your target audience. For instance, if you offer a free pound of coffee, only those who drink coffee will be interested and thus you have qualified a prospective sales lead. There are many benefits to having a free online contest. You will generate repeat traffic and add yourself to bookmarks very quickly. When these folks are ready to buy, your client will be remembered.