Linked from
The 22 pages that link to Yolk, each with the reason it gives.
CustardBroader topic: Yolks give custard richness and help stabilize its mixture of fat and water.
EggBroader topic: Yolk fats soften mixtures, while its lecithin helps bind oil and water.
Eggs as foodBroader topic: Its lecithin helps bind oil and water in sauces and batters.
Fried eggBroader topic: Its fat-rich contents thicken more slowly than the white sets.
OmeletteBroader topic: Its fat enriches an omelette and helps give it a tender texture.