Brainbell.com has a cool tutorial on a unique use of conditional formatting in Excel. How and when to use this method is only limited to your creativity, but I can see it being useful for applying a format only when printing a document.
From the tutorial:
The checkboxes from the Forms toolbar return either a TRUE or FALSE value (checked/not checked) to their linked cell. By combining a checkbox from the Forms toolbar with conditional formatting using the Formula Is option (shown in Figure 2-1), you can turn conditional formatting on and off via a checkbox.
Figure 2-1. The Conditional Formatting dialog with the Formula Is option
The whole routine is a little involved and pretty nerdy, but the results are super cool.
Have a look for yourself: Brainbell.com: Control Conditional Formatting with Checkboxes