What does configuring the When Workbook Opens option for a parameter limit a user to?

Configuring the "When Workbook Opens" option for a parameter limits the user to selecting only values that were present in the data at the time the parameter was created. This means that the parameter is populated with the values based on the underlying data source's snapshot, which reflects only those values that were available at that specific point in time. By doing this, the choices in the parameter are static and do not dynamically update with any new values that may appear in the data after the parameter was established.

This functionality is particularly useful in scenarios where consistency is required, such as maintaining the integrity of reports or dashboards that rely on historical data. Users can only interact with the values that were present when the workbook was first opened or created, ensuring that their choices are limited to known, stable data points, thus avoiding confusion that can arise from real-time data updates.