Doug Carter wrote:

So I wonder how often using "Compassion" or "Angel Flight" makes a
practical difference?

Controllers with whom I have spoke stated that they try to give a little
extra attention in the form of more direct routing, work-load permitting of
course. I have encountered a couple of controllers who didn't know what
the NGF/Angel Flight callsign meant and there have been others who
mistakenly assumed it got the same priority handling as Life Guard.

Personally, I fly for Angel Flight Northeast and often take flights
into/out of Boston Logan and Teterboro, NJ. I file with the Angel Flight
callsign for no other reason than to demonstrate to the controller that I
am not just another FLIB out for a $100 hamburger through their extremely
busy airspace.

--
Peter