I'm not the biggest spreadsheet fan but they do make data easy to understand for people who don't understand data or programming. You can have a visual representation of the data itself with the mathematical formulas and results all on one page. They also make entering data easy. Being able to just whip up a spreadsheet in a few minutes to show calculations to someone who isn't tech or math savvy is useful.

That being said, for my own purposes I'd rather use a programming language + file/database representation of the data.