How does a splash of vinegar help when poaching eggs? What does splashing in a shot of white vinegar to the simmering water do when poaching an egg?

Is it for taste or is it supposed to react in some way with the albumen?
Vinegar and salt both help the proteins (albumin) to denature (unwind) more quickly and link up to form a network of proteins, thus setting the egg.  The quicker the proteins denature the less feathering there will be around the edges and the nicer looking the egg.