I often find myself wanting to be able to switch between different chart types and options. For example, I frequently want to give my users the ability to switch between seeing a chart segmented and and not segmented, or to view it as a Line Chart, then a Pie Chart.
It would be wonderful to be able to control that with a formula that references a control (a button, checkbox, or whatever).
My users are not used to interacting with Coda, other than with the buttons and text I give them in the main document. So changing chart options is not something they will likely discover on their own. Therefore, offering them the ability to control these chart options with formulas would be a useful addition.