Well, I personally buy guides more for the visuals. Like when I started playing Tomb Raider Legend, trying to find the artifacts, even with Gamefaq's help, was not fun. Got the guide, everything was much easier because they had pictures/maps/screenshots. Same thing goes for Metal Gear Solid 3 and the Kerotans. So mostly I get guides for games where I need to collect stuff.
Also, for anyone wondering, the guide is being handled by Piggyback, and only distributed by Prima. And from the Pb guides I have experience with, they tend to be pretty detailed and have a bunch of extras like concept art and interviews. Actually the Tomb Raider Legend guide I mentioned is from PB.