Another point to add to this, I read many articles online every day and given the vague task of recalling these articles and what I took away from them I couldn't. But if I'm discussing a topic or listening to a talk on something everything relevant I've read feels front of mind again and allows me to draw new conclusions from what I've read that I wasn't really able to earlier without them all front on mind.

Really handy when, In a lot of topics relating to the kind of topics frequently on hacker news I can have long and insightful conversations with people where I have plenty to contribute myself.