People benefit from eggs. They are a cheap, quick protein source. They also contain nutrients that certain populations do not get enough of. Lacto-ovo vegetarians, who include eggs and dairy in their diets, can rely on them as a source of B12, a vitamin that supports neurological functions like memory, decision-making, and balance. Aside from fatty fish, eggs are one of the only natural sources of vitamin D in the diet. (The form of vitamin D present in yolks might be more potent than previously thought.)
People who live in northern climates, and especially those who work indoors, may lack the ability to produce sufficient vitamin D, due to limited sun exposure.
Eggs are also one of the best sources of choline, an important nutrient for fetal brain development that most pregnant women do not adequately consume.