Originally Posted by chessman

Notably, for the USA, it's only international flights. Bags can (and do) fly unaccompanied on domestic flights when the separation isn't voluntary. As an amusing example, I had a flight last year (MDW-PHX on WN) that got delayed and ultimately cancelled due to weather many hours after check-in. The airline didn't pull bags and sent them (including the checked car seats) to PHX the next day.

But WN didn't have any availability the next day, so we booked with another airline and, not knowing when our bags would actually show up, checked in additional car seats. The bags arrived a few hours after we did and after duly retrieving them we had twice the number of car seats as children. This led to a bit of a clown car scene at check-in on the return as I kept pulling car seats out of the rental car.