Microsoft Auto Recover
A very useful feature Microsoft added a few versions back is the AutoRecover feature. This feature is on Excel, Word, and PowerPoint, and is very useful if there is a power outage and you did not save the document.
How does it work?
The Auto Recover feature is turned on by default, and basically saves your document, automatically, into a temporary location after a set interval. To view the AutoRecover settings, click on File, and then Options. Click on Save, in the left-hand menu, and you will see the AutoRecover option, under Save Workbooks. By default, AutoRecover information is saved every 10 minutes.
Once you log back onto your machine, and open up the application you were working on, you will be presented with a Recovered Document. From here, you can either save the copy as the new working file, or save it as a revision.