The policy on tagging doesn't seem entirely clear with respect to when a question should have the author tag, when it should have the series/universe/work tag, and when/if it should have both. Since the tags are a useful tool, it seems like we should try to use them consistently.
I don't see any reason not to tag a question with multiple tags that might overlap but are still helpful and accurate.
Tags are a user convenience to help us search, select, and talk about broad categories of information regarding our questions. In the real world, categories are fuzzy and often overlap. Tags are for users, not for the system.
EDIT 2: Regarding authors, I don't believe that author tags should solely be used for referring to the life or circumstances or such of the author personally. Although they can be so used, an author tag can also be used for works written by that author. Why not?
Given this, tagging a question about something in Twilight as stephenie-meyer twilight vampire is redundant, yes, but it's not a bad kind of redundancy. It's not like we'll run of of tagspace or something. And it just might help someone find a question they otherwise wouldn't have -- which IMO is a good thing.
EDIT: Regarding the "geekspeak" issue as to whether tags should be normalized and whether unnecessary data is a problem, I respectfully submit that is not a problem for the users of the system. Although it may pose a challenge for implementers, from a user's point of view redundancy can often be a helpful thing.
As an example, consider a new user, someone new to SFF, who does not know that Philip K Dick was the source for Bladerunner. Is there then a problem with tagging a question philip-k-dick and blade-runner? Although the author tag would add no extra value to someone who already knows they overlap, to this new user this is actually useful tagging.
I've always understood that you use the ones that apply; for instance, if your question pertains to just lord-of-the-rings, then you use that tag. If your question is on the whole body of J.R.R. Tolkien's work, or on Tolkien himself, then you use tolkien, which is far more concise than say, the-hobbitlord-of-the-ringshistory-of-middle-earth and so on ad infinitum.
In general, when searching for something, you want to avoid having unnecessary data. Otherwise, when you search for questions about tolkien, the author, you find questions that have nothing to do with the man, or are only regarding a portion of his work. Adding an author tag to every question dealing with an author's work is a lot of unnecessary data: it effectively destroys the integrity of the author's tag. It may look nicer to us OCD types, but what is conveyed by a question tagged twilight stephanie-meyer? It should indicate that the question is not just about twilight, but also about the author of the series. If the question pertained to Meyer herself, such as "How did Stephanie Meyer's Mormon background influence the Twilight Saga?," tagging the question stephanie-meyer would be appropriate.