If 80% of the benefit is all you need and can be had for 20% of the effort, then do it. 

Learning to effectively skim and comprehend a reference book is one such example. For each chapter, read the first paragraph, the first sentence of each subsequent paragraph, and the last paragraph. Repeat for each chapter. Read all summaries. Take note of any important figures or tables. You will be amazed how much information and understanding you will absorb and how fast you will do it.

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