What is it usefull for?

https://elrond.com/blog/maiar-exchange-mex-tokenomics/

probably similar to other decentralized exchange tokens like uni, revenue sharing and governance voting i guess

Can refresh clear your cache and start again?

You get more tickets, and staking also gets you more POLS power, which increases your chances of winning... For detailed info on POLS Power, please read this: https://blog.polkastarter.com/all-you-need-to-know-about-pols-power/