BI-Discussion-Decision Modeling and spreadsheets

 Decision modeling with spreadsheets is regarded as clearly the most popular end-user modeling tool. Explain vividly why this is so, i.e., why a spreadsheet is so conducive to the development of Decision Support Systems (DSS). In your discussion, please include what a spreadsheet is, what a spreadsheet add-in means, and how can a spreadsheet add-ins help in DSS creation and use?