The properties of the yolk lecithin are appreciated to give their total consistence to sauces such as mayonnaise.
Lecithin enables to optimize water/oil mixtures. It also contributes to the good keeping of the recipes (air humidity) and to make demoulding easier. In powdered products, it enables the evenness of the grain (lumps) and for the frozen products it limits the ice crystals formation.
The natural pigments of the yolk are particularly looked for regarding biscuits and pastries.
For instance, it enables to get the golden aspect of the Viennese pastries after cooking.
The yolk enables to add taste to recipes and to "capture” other flavours.