Campaigns allow you to track your advertising of ClixSense.
For example, lets say you want to advertise your ClixSense referral url at a classified ad site.
You can create a campaign for it, use that referral url, and then check the campaign stats to see if and how many have clicked on it.
It can kind of give you an idea of what is worth doing and what is not.
For example if you want to advertise several places, you can set up a campaign for each one, which will be a separate ref url you can track for each one. So if you see you get 100 clicks from A, and 0 clicks from B, you know that B is probably a waste of time.