As others have already pointed out, the book contains a lot of sound advice that may not be ground-breaking for advanced programmers, but is useful for just about everybody.



Overall, the most useful aspect of the book is that it quantifies all of the optimizations that it proposes. I don't feel like designing test-cases to profile every single loop that I write. I also want to avoid premature optimization, because we know how bad that can be. Once you have assimilated Zakas' book, a lot of these little, day-to-day decisions will just come naturally: what kind of loop to use where, whether you should use a timer for some lengthy calculation, etc.



Execution speed is going to be a major consideration as javascript applications become more and more complex. This book definitely helps you think in the right terms.