Rather than having lots of different copies of worksheets to look at different options on your spreadsheet you can use scenarios to keep them all together and create a useful summary. This is useful, for example, when you have a budget and there are a number of different variables. A lot of people make copies of the worksheets to make comparisons.
Although this tutorial uses Excel 2003, it works the same on 2007 and 2010 the only difference is that you have to start it buy going to the Data tab on the Ribbon and clicking on the What-If Analysis button and choosing Scenario Manager…
Gary Schwartz's Blog 