Living on muscle meat alone can cause a copper deficiency via zinc dominance. It only takes a small ampunt of liver regularly to balance out the zinc in muscle meat.
Discussion
I love putting a little bit in my burgers or tacos. My wife, who is pregnant right now and doesn't like the taste, even finds this to be a great way to eat it.
I used to have tons of skin issues, and liver supplementation was a big part of clearing up the last of my eczema.