I wholeheartedly recommend this to GMs of ANY fantasy RPG! It is an excellent general-use GMs toolbox, both for preparing homebrew adventures, and for adding content to published adventures. It is also VERY useful while playing AT the table, where I use it a lot. To me it reminds me of the 1e AD&D DMG (all the charts at the back of the book), but Raging Swan Press' Dungeon Dressing book is just (to me) MUCH more directly useful, and it VERY well organized. Besides LOTS of random tables containing A LOT of solid and imaginative content, there is also a lot of very useful CRUNCH information in this book.
For ANY Pathfinder GM I really would consider this a mandatory GM's ressource. It is so good, that I personally consider it the number 1 "DMG" for Pathfinder! (I almost wish that Paizo got to publish it as an "Gamemastery Guide 2", so that more people would get it!)
TLDR: Get it if you are a Pathfinder/D&D/any fantasy RPG GM! You won't regret it, I am sure!!
PS: I can also REALLY recommend that you look at the Wilderness Dressing book and Scions of Evil (superb NPC collection), also from Raging Swan Press.