Well I do read the book, especially when I'm reading for myself. When I'm reading for others, sometimes I'll scan the book meaning, and by that I mean all of the description not just the bit under "starter readings" and different things will jump out at me. For example with Losgunna, the "starter reading" tells us (among other things) to pay attention to our dreams and go and have a hot bath. But sometimes the bit about life being boring for boring people and adventurous for adventurous people sticks out. So I run with that meaning. Other times I hear the bit about kissing frogs to find princes the loudest. Basically the book meanings for me provide jumping off points.
As I don't always have the book with me when I do readings with the Faeries I don't always refer to it. Sometimes, especially when theres a lot of cards in the spread, just the keyword/themes are enough to start me off on tangent. By now I have memorised all the keywords, well pretty much anyway. Er thinking of tangents I seem to have gone off on one.
To answer your question, I think any time is a good time to read the book. I love Jessica Macbeths wisdom and her phrasing. Often she's explained something in a way I understood but didn't have words for. I also like the way she describes the cards reversed. When reversed the energy of the faery becomes either blocked, twisted, or destructive, and of course its up to your intuition to decide which. Admittedly I don't actually use reversed cards but I do use spreads with cards in negative positions and these I read as reversed.
I think because each card has so many meanings, by the book, you still have to use your intuition a great deal in order to hear the 'right' message. I also think it was through reading the different book meanings (and of course here at ATF) that I expanded my original ideas of the Faeries, rather than just my idea based on the art alone. Of course, I am about a million times more verbal than visual so that may be why that worked for me.
So yeah, I vote for read the book.
FGM