Mentioned in a webinar? Not that I'm aware of. Then again, I've not watched each and every webinar, so who knows?
No, it's from personal experience working with it. As I was still fuzzy on it (it's been a few months since I played with it) I set up a situation to test. And it's as I expected. Here's the deal.
I tagged entire topics with tags. I configured filters and looked at the output. As expected, when filtering, the topics that should have been filtered out were actually filtered out. The problem with it is the Books in the TOC. The topics get removed via the filter, but if all topics inside a book are removed, the book remains. So you have to be sure to apply the tag to the book. You can get away without tagging the pages inside the book, but the books themselves need to be tagged or they won't perform the super duper magickal disappearing act!
Perhaps that simplifies it a bit?
Cheers... Rick