That David Mamet has firm views on any subject he addresses in print is a given - this short tome being his views on filmaking is no exception, being a short series of lectures on filmmaking he gave at a US university, though at times they do not read much like any lecture you may have attended!
For Mamet as a script writer, the story is key with his love of older movies for this aspect showing continually. Getting the beats of the acting, visuals, editing of scenes and ensuring these do nothing but support the key motivations and storyline of any scene and script is the key discipline to be learnt under filmmaking by Mamet. While at times he overstates some of his points, and reconfirms his dislikes of Hollywood and its inability at many levels to understand what makes a great movie plus method acting with its over emphasis on "what is my motivation?", there is a major lesson that is pretty well thumped into you by the time you have finished this book. That is be endless in your focus of questioning what are you trying to show or get to in the story through any dialogue/camera shot/visual edit/sound addition. The end result will then become an automatic process of continually challenging your team and yourself with "Do I really need this?" and "If I do this, what does it really add?" on everything and paring down to the essence of the story.
Applying this to each scene in any film will in turn make the whole movie better simply because you will have discovered the overall story you want to tell and how. The loser will be all the superfluous concepts and motives that many filmmakers burden and overload their films with, which in the process simply confuse or are irrelavant. For that very hard to learn lesson alone, this short book is worthy of being read by all filmmakers.