It is very clear that they are useful but it is also very clear that they can be problematic. In Finance people check each number - multiple times per day - because there is no way to write tests in Excel. Sounds good? Until you can trust the people crunching the numbers, of course. Would you build a bridge like that? Or a building? I think it is worth to talk about this problem and, at the very minimum, inform people there are alternative ways to crunch numbers that are more reliable than Excel.