I have in my kitchen + living-room one clock based on NTP on a dashboard, one on a WiFi radio and one on the oven.

Depending on where I am I see one of them so all must be synchronized to the millisecond so that children are not late to school (school is nearby, which exponentially raises the risk of them being late because it is just "4 minutes" away).

This is one of the scientific uses of such multiple clocks.