Yes, I understand that Docker caches layers. Like I said, if docker system prune is clearing a huge amount of space, it's like a large number of different image

Yes, I understand that Docker caches layers. Like I said, if docker system prune is clearing a huge amount of space, it's like a large number of different images and containers that might not share layers. If you're build, running, starting, and stopping containers all day, you might not be terribly careful about exactly what you're doing each time. That's why system prune is so useful.