Grocery Ads - Are they worth reading?

In the computer age of technology and Internet, have you ever wondered why it is that we still receive so many ads in our mailbox, whether wanted or not? In particular, it seems as though groceries find an abnormally strong return on their investment to send us (the average food consumer) advertisements in the mail. Why is this the case? Do that many people actually read these advertisements? Do people actually choose to go to a particular grocery based on the grocery advertisement they received in the mail? Are Grocery ads really worth reading?