Wasting paper and toner with empty staves

Almost four years ago, I digitalized the "Hauptsatzkantate". This cantata is about the fundamental theorem of calculus and was composed my Friedrich Wille.
In the original the empty staves are always hidden. When the piano does not play, you do not see any notes and this is also true for men's or women's voices.
This is very effective and the original, File "Hauptsatzkantate original.pdf", only contains 8 pages. If make all empty staves visible, then you have 12 pages, one third more. You will see it in the "Hauptsatzkantate mit leeren Systemen.pdf".
You can save much toner and printer paper if you hide empty staves in your compositions. It is even better for the environment, at the end.