Yeah. There are only two good reasons that I can think of to fill out a blank chart.
1) To preserve the family's history in someone's writing. It would be nice to have a genealogy chart in Grandma's handwriting. That won't work for my grandchildren. They would probably rather have one they can read. But it might be a nice idea in your family.
2) You know I had another one--that you would understand a file better if you look at the details while you fill out a blank chart--but I think I would rather spend my time looking over an already printed chart, color coding and adding notations, and then moving on in the research.
So I guess I really only have one. People ask us for them, so we have them--in case your Grandmother wants a writing project. Or if you have another good reason, let me know.