[Paraview] difference between types of mesh

[Dan Lussier]

I was wondering what is the difference between a Polygonal mesh
(vtkPolyData) and Unstructured mesh (vtkUnstructredGrid)?

I have seen both come up in Paraview examples for seemingly similar
data (i.e. unstructured points for example).

Is there a significant difference in their capabilities? Is there a
big advantage using one versus another in terms of memory allocation
or ability to be processed by different filters?

Thanks.