My hens are tri-purpose. Friendly entertaining Pets/Eggs/Eye Candy(just luv those big fluffy butts!). All the efficiency I need. But if you goal is just eggs or just meat by all means go with something uni-purpose. Leghorns, errr skinny butt mixed with over-sized frostbite susceptible comb mixed with flighty, just ain't my thing.I couldn't agree more! I still have a scar on my knee from a RIR rooster that nailed me when I was a teen. OFF WITH HIS HEAD!
This is just my own personal BIASED opinion. If you want chickens for laying eggs, get a layer. If you want to raise them for meat, get a meat chicken. The dual purpose birds are just not as efficient at either one. I don't know why more people don't keep a leghorn or two for eggs. They are awesome layers. Some folks say they are flighty, but I don't think mine are any worse than a lot of other breeds, and they can't be beat when it comes to cranking out eggs on a little bit of feed, even less if you free range them.
Of course I've got quite a few "useless" chickens, other than they are pretty and I like to watch them scratching and pecking around in the yard.