Parameters are a powerful way to give viewers control of how data is calculated on a workbook. Parameters replace constant values in equations, allowing viewers to dynamically update inputs. They can be changed on the fly within a workbook.
What-if or user-input analysis lets users explore different scenarios, and parameters make setting it up easy. By changing the value of the parameter, multiple visualizations can be updated showing how different inputs affect the outcome. You can set up a parameter for expected increase in sales and see how changing the expectation changes the sales forecast. A parameter with the assumed cost can be quickly updated as prices fluctuate. Multiple parameters can be used in the same equation, letting you set up flexible scenarios. The possibilities are endless.
A workbook showing segments or cohorts also benefits from parameters. Let users choose which segment to focus one, and all the charts on the workbook can update to show that particular segment of the total population.
The usefulness of parameters goes beyond these specific examples though. They can be used any time you want to be able to dynamically update values that affect multiple equations in a spreadsheet. Parameters can be text, number, or dates, and can be open input or a defined list.
Parameters are defined in a control element. Once defined, they can be used in formulas just like column names are.
Once you get comfortable with parameters, you think of dozens of ways to use them.