Just for the sake of not giving half truths, you have see look at sheaths in a breed context. What would be considered a poor sheath in a hereford or angus would probably still be a very good sheath in brahman influenced cattle. I'm not saying the breeds with good sheaths should let it slip, but there are more important traits to improve than getting a fetish over sheaths in most all British and Continental breeds. As long as it's functional, won't shorten the productive career of the bull and not emphasize an existing problem in a herd, I say keep working on the other traits that needs improving while just keeping an eye on sheaths.
As is the case in all traits, overemphasis on sheaths can lead to breeding tight hided cattle that will tend to be harder doing and of the dry muscle, dry bone type, so always keep the balance when making breeding decisions otherwise you'll end up losing more on the other end than what you're gaining on the end you're working on.
To stare yourself blind at a sheath that may not be ideal, but still very acceptable in any breed and miss the bigger picture of an outstanding beef bull, tells a story, too.
