Often the users need some guidance with the apps you create. Alot of my time goes in to educating the users. If there where some help text that you could show to the user that would cut down on some of the time educating the users.
Descriptions for measures/dimension can only be access if you are editing a sheet. Why not add them to the tooltip when you hover over a column header/the legend or labels.
Visualisation don't have descriptions at all. And the sheet descriptions are not very user friendly and hard to access.
I also would like to see an help icon when hovering over an visualisation next to the maximize icon that shows some additional help/instructions for the user. Or/and a button for the sheet that shows a layer of help text overlay on the sheet.