See cell actual data when hover the indexed name on the Formula tab
It would be really awesome when you're writing a very long formula that involves the data of several cells to see the actual data of a cell, when you hover over it name on the formula tab, so you know what you're doing without leaving the formula tab and navigating a very long sheet to see if that was the data you were trying to use.
Uncle Bob commented
Hovering is a nice idea. Complex formulas with nested parenthesis are a real pain. Right now, Excel changes the color of the parenthesis which helps a little but not much. In my dream world, Excel would have a "zoom box" feature the expands the formula with nested indents and other graphics like braces and lines. Then, the hover option would be truly great.
Gareth Hayter commented
Until Microsoft adds something like this to Excel, you can use the Formula Explorer in the free FormulaDesk add-in: http://www.formuladesk.com