Its not about " free thing", its like, you run a store, and have 2 valuable customers. First buy 2 things for total 50 $ every day, the other buy 10 things for total 50$ every day. Exact same amount. Then you go to first customer, with the second nearby and watching, and say "you have been such a loyal customer, here, have a free beer", while the second gets a smile from you. Its not about a beer, that costs nothing, but it gives second customer a feeling that he is less appreciated.