The Uk is thinking about leaving the EU. Campaigns run to see if Britain would be better inside or outside the EY seem to address the advantages for Britain. The most significant advantage for the UK is that without the UK influencing the EU, the largest market in the world may not work as well as it does with the UK.
The EU needs the UK. Without its “Westernising” influence, it’s connection with the USA and the English language, it reduces the EU. Being a part of it, and influencing it, the UK of course benefits but if the UK left the EU, although it may experience certain advantages of independence the greatest loss to the world would be that of an integrated and successful EU.