My tongue-in-cheek mention above of running all trains at 5 MPH to avoid collisions obviously was absurd. But not too many years ago, the idea of NOT kicking cars would have been placed in the same category. With the volume of traffic that railroads used to handle in some places, kicking cars the only way you could survive.
I was a yardmaster at a meduim-sized flat-switching yard. We had a crew at each end, and while they did have other work such as servicing cabooses, switching the repair shop, and occasional firm work (customers), most of their time was spent switching and making up trains. Many, many shifts, I would come in to a full yard, the crews would switch hammer and tongs, and at the end of the shift the yard was still full. It was not unusual to hold a train out while the yard crew cleared a track for it to pull in to. If they had not been able to kick cars, the whole place would have come to a halt from gridlock.
In fact, that was exactly how the guys exerted a little pressure if needed. Once in a while there would be an attempt to eliminate early quits or something, and the crews would slow down. The logic was, there is NO signal in the rule book for "kick", there is nothing in the rules or union contract saying a kick exists. Therefore, the company can't force us to kick, and can't discipline us if we don't. Every car was shoved to a hitch. And in no time flat, the yard was plugged, customers were crying because they did not get their cars, the dispatcher was wild because trains were being held out of the yard blocking other tracks. Usually it was a very short time before things were adjusted and kicking resumed. But with today's volume, 50% reductions in output are acceptable, and not serving the customer is no longer the sin it used to be. (maybe THAT'S why traffic volumes are down).
Pennsy - that would have been a neat thing to see! And again, as you mention, it was a routine move made countless times. No doubt once in a while there was a problem, but in the long run it helped speed traffic on its way just a bit quicker.