Rendering time on structured grid

Hello, so i’m using VtkStructuredGrid to render 3D grids and i need to make rendering speed tests to compare vtk with another tool, but i saw after a few tests that when i blanck a part of the cells like i need to do with the data i collect, the rendering time is way longer than when i only render the grid alone, i would like to know first why? and then if you know any solution to faster render a structured grid, i thought of using a decimation filter, but when i use the geometryfilter on my grid it transforms the cells into points only and i still don’t know why?
Thanks for any help that you can provide me!