Why Share? Triangle Strip as an Example of Sharing
In a triangle strip of 500000 <Polygons>, there are 1.5 million <Vertices>, if none of the <Vertex> instances are shared.
In a triangle strip such as this, only 2 <Vertex> objects could not be shared, so sharing gives us 500000 <Polygons> * 1 <Vertex> per <Polygon> + 2 <Vertices> = 500002 <Vertices> with a savings of 66%.