I had to google this since the only thing I could think of was durability. [Apparently there are a ton of disadvantages to paper bags](https://science.howstuffworks.com/environmental/green-science/paper-plastic1.htm) I feel like the Costco method is great because they reuse old boxes rather than try and get new materials. There are probably disadvantages to this as well, but I have no idea what they'd be.