It allows you to see what files are contained in the package, and then you can do an uninstall of the package if uninstall is enabled for that package.
It's been handy for me to find what package has a plist that shouldn't be in there. For instance, we had a number of computers that the airports were having their properties changed from what the base was. I searched for the airport config plist and found what package had it in there and was able to edit the package and fix the issue.
-John
