Yeah, well, you see these books recommended all the time. Some of them have been on the shortlists for decades. I'm not convinced they are adding rating points.
You read something like Understanding Chess Move by Move and it's yeah, great, nice move GM...and thanks for telling me why they did that, Mr. Nunn.
But it doesn't make YOU a better player. You can watch golf and see Tiger Wood takes his 5 iron out, and have the reasoning behind that carefully explained to you. Doesn't mean if you are at the same place on the same course that your five iron is going to help AT ALL.
There seems to be an assumption that if you stare at their play enough, and have someone "explain" it to you, eventually osmosis will kick in and your own much more limited set of chess skills will absorb theirs.
I say...NO. That doesn't happen. Studying GM games will not make you a better chess player. It will make you a better chess enthusiast, fan, or reader. But your OTB skills will not significantly improve...because you will never think like they think.
You can learn to play piano, but it doesn't matter how often you listen to Horowitz, or watch his fingers move...you will never play it at his level.
Studying master games can be extremely beneficial, if they are annotated at the right level for the reader. The most useful for beginning and intermediate levels are "instructive annotated game collections" like Chernev's The Most Instructive Games of Chess Ever Played: 62 Masterpieces of Chess Strategy or Reinfeld's The Immortal Games of Capablanca.
Newer works of the same kind include many Everyman publications (which are also available in chessbase and PGN forms) like Chess Secrets: The Giants of Strategy: Learn from Kramnik, Karpov, Petrosian, Capablanca and Nimzowitsch, by Neil McDonald (everything he does is highly recommended), and the great Understanding Chess Move by Move, by John Nunn.