The biggest benefit of my local dns server is latency. On wired internet, my dns is <1ms from my PC.

Upstream dns for me is pretty quick. Google and cloudflare dns are ~5ms from me. But WiFi latency alone is ~8ms most of the time in my experience. On my fiber internet, pinging a dns server in some random upstream server miles away is lower latency than WiFi 10 feet away. But the real issue on WiFi is any packet loss at all adding 50-100ms to that at random depending on interference.

With DNS you are paying this latency cost all the time on nearly every request.

This will be slow for one user, let alone more than one

“The trick everyone misses”