“The first reason for this is that forgetting is a filter. When something you read resonates with you sufficiently for you to recall it without effort, that means something; it means it connects with your ideas and experiences in some relevant way. Replace that natural process with a more conscious, willpower-based system for retaining information, and you risk losing the benefits of that filter.”
I've started reading more slowly and a few years ago I dropped a lot of the underlining and highlighting and just read books. Occassionally I dog ear a corner of a page for something, but not too often. And if I'm still thinking about something I read a few weeks or months or years later, that's how I know it's meaningful. That's what's led me to reread, to see why I keep thinking about certain stories and concepts.