I've seen it before. it's hit or miss really.

I was on a flight (SAN-MSP) that landed in DEN due to a medical emergency. As we were approaching MSP the pilot announced that two flights had been held back, one was to EWR, not sure where the other one was and the flight we were on heading to MSN (I think) had already left.

Me thinks they went over the pax list and saw a large number of connections to those two chosen cities, or, the later flights were grossly oversold that the missed connections wouldn't be worth it and it's feasable to hold flights for a few extra minutes.