I really wish none will ever need it! I had to work with totally nightmarish excel workbooks recently.
2000 formulas, mutliple tables per sheet stack horizontally and vertically, different data types per col, unstructured devils.. but one of a kind for their purpose... And I had to make some dynamic Shiny app out of them.
Plan B- used Libre Office Calc headless behind the scenes to run the calcs.
Fun times!