It should be used before designing the actual test plan and allows to identify (bug) risks. One benefit of using it would be to focus scarce testing resources on high risk and high impact risks first. I highly recommend this article by James Bach for the full background.
Also I'm proud of the new outlining feature. It allows you to add some graphic file to your test project. It should be used to describe the test plan and process in a graphical way.
Both features are optional and must be enabled per project:
A risk analysis could look like that:
For example I know that testing with non-admin user account can find certain bugs, but I think that for the application under test this is unlikely to occur, so I wouldn't invest time in that.
And this is how the outline looks like with a practical example:
It's really just an image you can link here. It maybe overlaps a little bit with the test strategy, but you could also document which component should be tested by which tester (group) or you could highlight key components and so on.
So it's really versatile.
The latest version can be downloaded from sourceforge.