What are the advantages and disadvantages of package sizes?

In the last two months, I have looked at ALOT of coffee websites, but I think I have only seen only a small fraction from around the world. Obviously, it is easy to find a variety of different bag sizes for sale. On Amazon, for example, with one click you can add three 1lb bags to your cart, but I have not seen anything for sale that only allows you to purchase a three pack. Right now, I only have three seperate bags for sale. Does only allowing the purchase of three separate bags affect consumer behavior? How does it make them feel? I would like to know the answer.