Eggs are used like a glue to hold ingredients together as they are coagulated when cooked.

Whipped albumen contain tiny air bubbles. When this mix is added to other ingredients, it makes the dish light and fluffy.

It happens when egg is overcooked and because there is a reaction between the iron in the yolk and the hydrogen sulfide released from the sulfur containing ferrous sulfide.

Beaten egg yolks will coagulate and hold a liquid in suspension when heated, changing the viscosity of the food item

Beaten whole egg or yolk brushed onto food items before baking will give it a gloss or shine.

Whipped egg yolks can hold other ingredients together that do not normally mix, such as oil and vinegar

the change in the structure of protein (from a liquid form to solid or a thicker liquid) brought about by heat

egg white helps trap air allowing the baked good to rise and be light and fluffy

Whole egg and breadcrumbs to provide covering or protection for the food item prior to cooking

Since the egg white and yolk are thicker than water and other liquids, egg helps flour, seasonings, or breadcrumbs stick to food.