Yes, I got into the habit of using books in this kind of instrumental way during my PhD, of just taking what you need and nothing more. It can't be avoided, but in the long-term it's healthy to select some choice books to read in their entirety, if only because otherwise you'll learn nothing new. There should be some balance between focusing on what's immediately valuable to you, and exploring new ideas. Books are also usually written as wholes, and are for that reason are often best understood when read from start-to-finish.