Here is why:
Many programs sending 5 cent emails to 10 cent emails are not going to pay you! They dont charge enough for the ads to pay more than 5 or 10% of people who click on the ads! How will you be paid when you reach the minimum payout? Chances are You Wont Be Paid!

If you dont know how to work out sensible ad prices you can use this tool to see a rough guide to what programs should charge for advertising so that ALL members will be paid when they reach payout