The author could have mentioned testing. The reason I use python scripts instead of spreadsheets for important calculations is that I can unit test the logic e

The author could have mentioned testing. The reason I use python scripts instead of spreadsheets for important calculations is that I can unit test the logic extensively and be sure that the code works as expected. This also makes sure I don't break stuff when adding functionalities / refactoring code. I would never ever use Excel for something important, unless it's completely trivial (e.g., sum/average values of a column). I assume the same applies to R vs spreadhseets, of course.