A typical model consists of several worksheets - Inputs, Revenues, Opex, Capex etc.
Imagine as well your model has three scenarios - Base, Upside and Downside which you can switch from and to on the Inputs sheet.
You set your model to Base scenario and start walking through it. At Capex sheet, you decide you want to look at it under the Upside scenario and wish there was a way to switch between scenarios on every worksheet.
The attached file explains how to do this.