The concept of "this is one of my favorite questions" seems simple -- but if that were really what "favoriting" a question was supposed to do, there would be rep associated with that action.
Because there is no rep associated with it, it makes me wonder... as an asker, what is a favorite supposed to tell me? What am I telling an asker if I favorite a question? Nothing at all?
I think the other question pretty much answers your question.
Most of the people that replied seem to use favorites like bookmarks (and I do as well).
So if you treat favorites like bookmarks, then by favoriting a question, you're telling the asker that you want to be able to refer back to that question in the future. That could be because there's a stellar answer you want to keep as a reference, or if there isn't a good answer yet you would be saying you're also interested in the answer. Or, it could even mean some people have unfinished business (examples given were wanting to vote when the daily cap has already been reached or wanting to revise an answer later).
Conversely, if your question doesn't have any favorites, than everybody who has visited it has already gotten everything out of it that they think they are going to get. That's not necessarily bad.
As I see it, the favorite star implies "worth revisiting, for whatever reason".
There are a few badges the OP will earn at 10, 25, and 100 favorites -- if you can ask a question that a lot of people think is worth revisiting, I believe that is noteworthy.
