Karnofsky suggests that the cost/benefit ratio of how we typically think of reading may not be as simple as we intuitively expect i.e. we think that 'more time' = 'more understanding'.
If you're simply reading to inform yourself about a topic, it may be worth reading a couple of book reviews, and listening to an interview or two, rather than invest the significant amount of time necessary to really engage with the book.
A few hours of skimming and reviews/interviews may get you to 25% understanding and retention, which in many cases may be more than enough for your needs of being basically informed on the topic. Compared to the 50 - 100 hours necessary for a deep, analytical engagement with the text, that would only get you to 50% understanding and retention.
That being said, if your goal is to develop expertise, both Karnofsky and Adler ('How to read a book') suggest that you need a deep engagement with multiple texts.