None, though to be fair this site is custodial and centralized. A similar thing could be done with fiat and existing legacy banking infrastructure. That said, if I cash out any sats they will go through a lightning node, and eventually end up in my own non custodial bitcoin wallet. There will need to be at least one on-chain transaction for me to close my channel and own my bitcoin. The main chain cannot handle the throughput necessary for everyone in the world to transact as much as I do, even if only for closing lightning channels.