Many years ago when I was a Watch Manager at Farnborough, we were told of a helicopter crash north of Reading and asked if we had worked the aircraft, which was stated to be an R22 and 2 bodies had been found in the wreckage.
I checked through our flight progress strips and found we had worked it northbound to Wycombe, but its type was given as an S300. Knowing that an R22 is a 2-seater but an S300 is a 3-seater, I checked with Wycombe ATC to see if they knew how many were on board.
The lovely Coral told me they had booked out with 3 on board, not 2, so I duly informed police and AAIB they should be looking for a third person.
They eventually found the third body some distance from the wreckage.
Had the airfield not required the pilot to book out, the search for the third person might not have been initiated; had that third person survived the crash (AAIB deduced they must have jumped out before impact) they might not have been found and could have died of their injuries.
Is that not a good reason to book out?