Hiding a header or footer in PBI RS will hide the content but it will still take up whitespace, allow it to be consumed to save space
When a report's header or footer visibility is suppressed on any given page, whitespace will stand in its space. Consume whitespace has no effect. This is a waste of space and can generate thousands of additional printed pages in large deployments.
Save the trees, save bytes, and save money -- please let us utilize the freed up space of a hidden header/footer!