How often have you heard someone suggest after reading a book:
“The point of this book could have been summarized in a few pages and didn’t need a few hundred.”
While this critique is valid of a large number of books whose ideas are simple and shallow, it often gives people an excuse not to read books. Even though almost all books can be summarized briefly, the true value to reading a book is spending time living with and dwelling on the ideas. This can only come from spending the time to read.
Our brains remember and deal better with situations or ideas that actually have more detail (consider that a story with more information actually makes it easier to remember than a story with little information). As a result, spending time reading a book allows you to remember and apply ideas to your life where as reading summaries just lets you look smart at cocktail parties. 🙂
All that said, some ideas are clearly not worth spending that much time dwelling on and therefore aren’t worth reading and in those cases, I highly suggest just getting the summary. But if the ideas are of sufficient quality, spending time dwelling on them is really the only way to truly understand them.