I was once told by a GA that the airline, in my case United, has a choice on which flights will be delayed due to ATC. For example, in the mornings at SFO, there are often ATC delays for arrival. United specifies which flights would be delayed and which flights would get priority. In my case, often the LAX-SFO flights get priority over the BUR-SFO flights. Anybody knows if that is true?