University of Paris professor Pierre Bayard, author of "How to Talk About Books You Haven’t Read" is a genius, at least based on this interview.
Not especially deep, but I found huge value in grad school (at MIT, we never really had to read), of skimming. That's how I stayed ahead in those political science and education classes that assigned two dense books of reading per class per week, while doing the course load for 3 degrees simultaneously.
Basically, I made sure to at least skim everything (when most of my classmates would get bogged down, and just skip). Sure retention goes down, but at some point, I learned that there is no neurological basis for forgetting. So quite possibly your brain potentially stores everything it comes across, somewhere, just you don't always have access to it. So I figure, if I stuff it full of stuff, even cursorily, things will come together if sufficiently important. Seems to have worked well enough to get A's in those fuzzy classes anyway.