In the early 1980's in the Frisco yards and outlying switching jobs, we bled off cars and kicked everything we legally could. When I worked on the QA&P board, those men liked to switch with air, and their engineers and firemen did something different: when a field man called for "cutting the air in" the engineer would give 'one short' on the horn and make a 10 lb reduction while we opened the anglecock. I didn't ask them why they did that...when you're in Rome you do as the Romans...but I have always wondered if that practice had some benefit. Since I never qualified for engine service, the question remained unanswered.
There were even instances when Frisco engineers came to QU to cover QA&P vacancies and they would comply to this practice without being told to do so. But when we returned to the OKC board, it was back to the usual. This isn't an earth-shattering question, but after 30+ years I still wonder about it.
Quien sabe?