Oxygen Dissociation Curves

Why is the fact that oxygen dissociation curves are sigmoid an avantage?

is it something to do with oxygen release?

yup it's completely to do with the way the oxygen is released. each heamoglobin molecule contains four oxygen molecules. the first oxygen molecule is released relatively easily but after this has been lost the shape of the heamoglobin moleciule changes and the next two oxygen molecules are released with more diffulculty. the final oxygen molecule is released more easily then the previous two. this explains the shape of the curve and is an advantage because it means that the heamoglobin does not give its oxygen away at the same time thus can respond to changes in the body when more oxygen is needed.

hope this helped