Most people who are only vaguely familiar with networking seem to be able to remember 10/8 and 192.168/16, but the 172.16/12 range is for some reason rather elusive --- I suspect it's not as commonly used as the other two.

I think it usually gets used by VM/container networks (maybe there's some historic reason)? I have seen it once used on a hotel WiFi network (as I was unable to connect because of docker conflicting).