If you feel that this app has a purpose that is "dubious" then do take a look at this list of apps that support metadata tags: http://code.google.com/p/openmeta/wiki/OpenMetaApplications
This might help to make the purpose less dubious.
Tags for text documents need not reflect the text contained in the document, it all depends on the reason for tagging. For example, a tag might be designed to identify documents relating to one or more projects, research areas, etc. (Aliases could be used to set up a directory structures to fulfill a similar purpose. However, using tags means that you can gather and analyse resources using other apps.)