There are all kinds of spreadsheets.
Big, ugly ones which always crash your system. Cute, colourful ones which are light on logic. Powerful, flawed ones which have a single wrong formula hidden inside.
Analysts stay up all night building spreadsheets. CEOs give bold presentations powered by the humming engines of spreadsheets. Companies make business decisions worth millions, even billions, of dollars based on suspect evidence manufactured by spreadsheets.
By comparison, napkins have much humbler origins. Most of the time, they are simple accessories to food and drink. But sometimes, they are magically transformed into powerful business tools.
What can be done on a napkin? Brainstorming. Mission statements. Values. Scenario analysis. Business models. Short term forecasts. Long term forecasts. Legal agreements. Illegal agreements. All sorts of stuff.
Simplicty is the biggest advantage of the napkin because this forces clarity of thought. The spreadsheet is powerful but the napkin is practical.
Napkins beat spreadsheets.