About "it's more work on their part": when I lowered drastically the number of my slides, and started to put emphasis on facilitating the creation by my student

About "it's more work on their part": when I lowered drastically the number of my slides, and started to put emphasis on facilitating the creation by my students of their own knowledge I had the guilty feeling of not spending enough time preparing the class. Preparing a lecture can be many hours of works. (Of course some lecturers will reuse ad nauseam the same slides and content for years. Not even thinkable in my field :-)