Short answer
Whites provide protein with very little energy or fat; yolks contain protein plus most of the egg’s choline, fat and micronutrients. Neither part is universally ‘healthier’. The useful choice depends on the meal and person.
What the white offers
Egg white is mostly water and protein. It can increase meal protein while adding relatively few calories, which is useful in some sports, appetite or medically directed eating plans. It supplies a narrower range of micronutrients than the whole egg.
What is concentrated in the yolk
The yolk contains most of the choline and vitamins A, D and B12, along with selenium, iodine, fat and dietary cholesterol. It also supplies part of the egg’s protein and much of its flavour and cooking functionality.
A practical middle ground
Combining one or two whole eggs with additional whites can increase protein while retaining yolk nutrients and flavour. That is an option, not a rule. Avoid discarding yolks automatically unless the nutritional trade-off serves a clear purpose.