Explain 80/20 pools tradeoffs

[ylv-io]

In the weighted pools it states that 80/20 is the best ration but no explanation why is given. I'd love to see some math and external sources. It is not clear what are exactly the tradeoffs in the 80/20 pools and how they relate to pools likes 70/30 and 90/10. Providing an external reference to the explanation would also work.)