Tags can be used to sort and filter in the sort and filter dialog. That's their main point of usefulness. In the "Custom Search Filter" dialog, after the field for text is a button to select one or more tags to include in your filter.
Personally. I dislike tags. I use them sparingly, and find text more useful. Many of the things that are tags (Race, Class, etc.) in Pathfinder are things I would prefer to have linked to the appropriate Mechanics content.. so I prefer to use text search.
With export and import, I imagine I will find tags more useful.
In a mystery game, tags for character descriptions and traits could be a useful tool for finding suspects based on witness descriptions and other clues.
EDIT: To expand a little, I think what people would like (I know I would) is something that presented Topics or Articles in a list to allow selection ... and avoid typos that prevent linking to them. Tags present the list, but they aren't a list of Topics or Articles (even though it is almost certain that some of them {Races, Classes, for example} would be based on the game system -- IF the mechanics were also loaded).
When working with software development, time and again we asked our users not to tell us what they thought the best solution was (such as "Tags as links") but to tell us what they wanted to accomplish (which, in the case I suggested, would be "avoid typos that prevent auto-linking") and let us suggest what we thought were workable ways to achieve that goal.
Sometimes, when I point out potential problems with suggestions, that's what I am getting at .. focus more on explaining what you're trying to accomplish and less on telling LWD how to go about it.