The paper guides often double as artbooks and "proper manuals" which make them nice to collect and read in the bathroom, as well as have on your lap whilst playing. I bought the original Dragon Age one, and found it useful and well written, especially given the minimal supplied documentation. Coming from an age when games used to have 100+ page manuals describing how the mechanics worked, I found it very helpful to read how DA's systems fitted together, and how the various skills, stats and abilities functioned.
Now, you can get most of this info on GameFAQs (or whatever), and I keep that around too, but nothing quite comes close to holding a paper volume (for me).
But yes, unless you're spending a lot of time with a game, and want to fully submerge yourself in it, then the guide probably is a waste of space. I probably won't bother with one for DA2 when I finally get round to buying it (waiting for an ultimate edition), since most of the mechanics seem similar to DA1, and from the little I've seen, it appears more linear and regimented with less side-content.