Reading through this thread, I am in part reminded what I refer to sometimes as the instrument being its own teacher.
Surely, a deck whose artist has intentionally overlayed various details, with these being understood in a symbolic manner according to specific views (no matter how historically inaccurate these may in fact be), has some 'claims' that such-and-such 'means' such - but out of the context of a specific reading only. For such, a book that specifically explains the context and framework of reference used by the designers of the image is useful in further understanding the intended deck design qua specific deck.
This does not mean that one needs to study other fields that have been overlayed onto tarot in order to understand and appreciate the flow of tarot that will still form the base upon which the deck is constructed. Hence in large part why I personally favour a tarot that avoids overlays: if I am interested furthering my understanding of tarot as tarot, then its superimposed layers distract from its essential qualities.
In terms of such, then, I am utterly in agreement with Umbrae's statement when he says: "out of all the books I’ve read, how many have helped me be a better reader [...]? Zip nada ziltch"
One of the best readers I have ever encountered knew not even how many cards were in her pack. In fact, she read tarot as she would read flowers: being open and responsive to sensory influx - much of which beyond the normal bounds of the lower senses, yet the reading still very much grounded in the specifics of the imagery, and utterly responsive to the person for which she read.
This does not mean that books are not useful, of course. Again, some not only provide, as mentioned by Umbrae, a better appreciation for tarot, but also, as berrieh mentions, may also assist in unlocking and unblocking what has frequently been referred to here as one's comfort zone and allowing a new 'ah AH!' episode into what may otherwise remain fixed or blocked - the book, in such a case, may serve as 'S-bend' cleaner (to use the metaphor introduced by Formicida above).
Whether by book, forum, conversation, lecture, workshop or myriad other forms (including usage of the cards themselves), what we are in part doing is, as Fudugazi says, learning from others. A book permits this interaction from speaker to 'listener' across space and time (as does, in a different manner, this Forum).
Yet, what is possibly of far greater import in the context of a reading (rather than the context of knowing something about the cards) is the engagement in the very act of reading. Of course one needs to be able to narrate, and such will be ever easier given a rich field from which to draw... in other words, broad education (irrespective as to whether it is formal or not), combined with reflected life experience, in a context that is communicable and hence in touch with the needs and skills for whom the reading is geared.
Can the many tarot books out there help in some manner? yes - and many may also do the inverse, of course. They can help if taking them as being no more than a conversation between author and myself, a conversation requiring, on my own part, active reflection and, importantly, discrimination.
In the context of a reading, the 'S-bend' in a toilet may be the most apt manner to narrate the card... and discarding its non-tarot additional overlay may enable, in the context, both a deeper appreciation of the card as tarot as well as focussing on the reading as reading.
