One of their slides (https://speakerdeck.com/eranyanay/going-infinite-handling-1m-websockets-connections-in-go?slide=7 https://speakerdeck.com/eranyanay/going-i

One of their slides (https://speakerdeck.com/eranyanay/going-infinite-handling-1m-websockets-connections-in-go?slide=7 https://speakerdeck.com/eranyanay/going-infinite-handling-1m...) lists the use cases for such functionality and they are pretty broad (message queues, chat apps, notifications, social feeds, collaborative editing, location updates). When you consider the price of the hardware and complexity of the system, it's obviously useful not just for handling 1M connections per host but also 10k connections per host. If some other technology / framework can only do 1k connection per host, then you can per 10x less for hardware and have room to spare. And the system will simpler which means faster to develop.