I love the Column Description feature. We use it to provide guidance to sheet users on how each column is meant to be used. It is invaluable to us!
It would be REALLY helpful to have the same feature for the Sheet itself. Before you even ask yourself what the column is used for, it would be helpful to understand the Sheet's purpose. I would love to see a little icon by the Sheet Name/Favorite Star that users could click on to provide instructions.
We have tried using either Sheet Comments or Sheet Summary to serve this purpose but it is ineffective. Only "Power Users" know how to find these features. Even when we explicitly tell them, it is hard for them to remember the navigation and it is not a good user experience. Casual users need something more intuitive and obvious.