I think it was JBiebs that introduced this principle to me first. I was back at Penn last year and we were having lunch. I was asking him for advice on what classes to take and how to get the most out of him. Something that stuck with me was what he said about how he always makes sure he has at least one key take away from the classes that he takes. One sentence that summarizes the most important concept he learned.
A few reasons I think this is a good concept to apply to several things are that 1) it really makes your brain reprocess the information that was thrown at you and that itself helps you retain information better, 2) because it's one sentence it's even more likely that you'll remember it, and 3) because of 1 and 2 you're likely to really have gained value from that one class or whatever.
Today I had several meetings in a row and decided that I might try using this "find a key take away" thing to see if it does any good. Immediately I found myself really thinking about the conversations I had more than I normally did. Usually I would forget most of the notes that I took. In addition, being able to synthesize it I am now able to really internalize the lessons and advice that was given to me. I think this is something I am going to continue doing.
And this shouldn't only apply to meetings with people who offer advice and guidance. But it can be used on a daily basis for all tasks. After you do some Google-fu for research, after you read an article on Hacker News, or after you finish trying to figure out what way to design your next batch of code. Next time I'm going to use this method and figure out how much it will improve my life and the amount I learn and retain what I learn. My hypothesis is that it will be really beneficial.