Never had the patience for it. Why create stories that aren't canon? I just never understood that. Part of the reason I don't read it is, I don't want to bog down my mind with ideas about things that are irrelevant to a show that I enjoy so much.
Can be full of complete trash, or they can be quite wonderful. I equate them to reading magazines as they aren't always challenging mentally, but they're fun and usually fast reads. I do worry that some writers have serious trouble with plot and character development to the point where they pretty much copy-paste the text and then insert their own characters. Those are the bad ones much of the time. The good ones are one where the text is only referenced and used as a sounding board and the known and unknown characters take on a life of their own.
"I took the one less traveled by,
And that has made all the difference."