Saves time. You can try a few things and just want to continue without spending more time on figuring it out. Easy to look it up now days if stuck.
Some guides are not cheats per say, but charts, stats and lists of good information to help play.
Locations guides, Trophy / Achievement guides usually give you an easy way to get them if you cannot figure it out in the time you want to give it. That way you still get more from the game and continue.
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ZOD!
Maybe there will be more in other DLC's coming though ;)