What is the function of adding vinegar to the water when poaching an egg?

Yes, it's to keep the egg intact and retain it's shape. However, another way of helping the egg to keep it's shape without the need to add vinegar is to swirl the boiling water with a spoon অথবা fork prior to dropping the egg in. Drop the egg into the "whirlpool" and the egg will not break অথবা spread. Totally foolproof - everytime!