I've kept all the little booklets, but only because I'm a tad obsessive about details (namely, keeping everything in the box or bag organized). That being said, normally I've found the booklets aren't especially helpful, and each one seems to give a completely different meaning. I have found one helpful (the one that came with the Ancestral Path Tarot) but again, its rather specific to the deck and wouldn't be of much use with, say, a Rider Waite.
On their own, they are full of a lot of insightful details, however: like tiny mediation books. But to interpret the cards, I use a combination of a trusted, offical resource (like a well-written guide) and my own intuition, rather than the sparse keywords in the booklets.