Reliable genetics. Good traits. I've never been able to get good queens with my local genetics. Of course it depends how many colonies you have. If you have hundreds you can select your own good traits from your good colonies. I only have a few hives so order my queens from Exmoor bees and Beehives. There is no comparison to their's and my local 'pot luck' queens. And then there is the delay while waiting for a queen to get mated, if the weather turns nasty, that might not happen. The queens pay for themselves in the honey sales.