Every reloader I know has several books, although I expect they have favorites. I find looking at similar load data from multiple sources (including, often, the Internet) helps me get a better sense of appropriate pressures and velocities. It also might help you be more conscious of bad data -- if two books seem to be significantly different, that's an indication that you need more research before trusting either (I've never seen really bad or dangerous data, but I've heard stories ...).
And of course, we should mention the need to keep your own data. If you loaded it, shot it, and inspected the brass (and especially if you chrono'd it), that's the best kind of reloading data to have for next time.