I eat the liver of the animals I butcher, basically my theory is that if you eat all the tissues of the animal, you are less likely to develop deficiency or excesses.
I eat a whole sheep liver every month, usually will eat most of it during the first week after a fresh kill, during that time I will eat a lot more and my digestion will kick into high gear, giving me abundant energy, toward the end of the month after going about two weeks without liver, or fresh blood or other organs I begin to feel signs of lower energy and slower digestion. Then when I get a fresh animal and drink the blood and eat a large piece of liver I feel immediately rejuvenated. There is an eb and flow to my diet, I store up on the nutrients of fresh organs and blood for two weeks, and then live off of mostly muscle meat and fat for the other two weeks, before being replenished with the next kill. In this way I use up my stores of nutrients more efficiently, and believe that there is less likely an issue with imbalances that may be associated with eating too much of one part of an animal or too little in another part.
It seems something that is totally necessary for me, though I warn that there was a time when I would eat extra liver bought from the store and would not feel so good after eating around a pound a week. One also must be sure to get good quality livers, I go by taste now, but when I was first starting I would eat store bought liver that wouldn't taste good and eat it anyway, and then would feel bad afterward.
Ive seen horrible quality livers come from so called grass fed animals, but what isn't on the label is the fact that it comes from cows who were dewormed with chemicals 60 days before slaughter, and fed substandard hay, and they come from stock breed that have been fed grain for many previous generations and may not be well suited to live on grass.
Now days if it does not taste good then I will not eat it.