It's more about keeping the line running. The line has a fixed throughput, and if it stops, it's hard to catch up. It's a stupendously expensive thing, staffed

It's more about keeping the line running. The line has a fixed throughput, and if it stops, it's hard to catch up. It's a stupendously expensive thing, staffed with a similarly-expensive complement of workers. Rework in the yard, on the other hand, is "soft", it can can be parallelized across as many workers as you can deploy, and they're usually contractors so you only bring them in when you need them. So if cars can be finished enough to roll 'em through end-of-line and then into yard hold, that's what you do. Clean it up as soon as possible of course, but whatever you do, don't stop the line.