Copper is a trace mineral you need only a little of, but that little does real work: forming red blood cells, keeping your nerves and immune system functioning, and building connective tissue. When intake stays low over a long period, that's been associated with tiredness, more frequent infections, and problems with iron being used properly, since copper and iron work closely together.
Genuine low intake is relatively uncommon, and copper is one where balance matters in both directions, because it has a real upper limit. Adults need only about 1.1 mg (1,100 mcg) a day, which most varied diets supply, from shellfish, organ meats, nuts, seeds, and dark chocolate.
The ceiling: it's best not to exceed 10 mg a day, since consistently high intake, almost always from over-supplementing, can be hard on the body. For most people eating normally, copper isn't something to chase, just something to get steadily.