I too was unfamiliar with the purpose of culling until I started breeding PFR's. I had one female with a flaw in her carapice. On either side of her head, she had a muddled spot that looked almost transparent compared to her rich red body. I mistakenly didn't cull her, and i found the same flaw in about 20 shrimp down the road. I had about 20 berried females in the tank, and thats not to say that she didnt produce any high quality offspring (there would be no way to know), but it took me a very long time to grow out those offspring to find their flaws and remove that gene. Just my two pence.