But for non-fiction books isn't the summary good enough?
I am thinking, in particular, of business books.
On reading an interview with Doerr of his new book (measure what matters), I feel I have a good sense of what is in the book and how to implement it.
Do I? Has anyone read the whole thing? Can they comment?
For something like "measure what matters", the basic idea comes through in the title. I would expect that a summary would capture things pretty well - it will omit some detail, but it will be just detail. The big idea is the point, and that comes through even in the title. I suspect that most business books are in this category, but I am not sure.
For some things, though, the details really matter. Take "The C++ Programming Language", for example. You could, maybe, write a summary of that book. Do you know anything from reading it? Not really. Too much of the content is details. The whole point is the details.
If the non-fiction book has merit, it usually includes the rationale and real-world examples of the thing explained. Therefore you can examine the idea and have a deeper understanding of the subject or even improve on the original work.
Summary forces you to memorize a few facts and you wouldn't even have a basis to evaluate the validity of the idea. I read summaries only when the book is written for the general public and I already have expert knowledge about the subject.
In my opinion, reading summaries give a false sense of accomplishment. Reading is not about understanding one idea and implementing it. It is about understanding how to reach that idea, therefore you can improve on it.