That's correct.

Just declaring a vertex index as a property (either bundled or interior, as here) won't buy you any new functionality. It just provides a place where you can assign an index for each vertex or edge. The problem that this half-solves is that nearly every algorithm in the distro requires a vertex index map (or edge index map, more rarely), and providing this will allow the default arguments to automatically extract a property map for vertices/edges.

It won't - or shouldn't??? automatically assign indices. Also, if you remove a vertex or edge, you may have to renumber vertices.