At prep night yesterday, we talked for a bit about players who take notes during our games, and how useful those notes can be for us as GMs. I usually have at least one player per campaign who enjoys keeping a pretty detailed record of people, places, things, events, etc, and I reference it all the time: I can check what treasure I've already handed out, what NPCs were memorable to the players, what points of interest they found notable enough to write down. It's super handy, and there's usually one player who becomes our "archivist" so to speak.
I've seen some people on here talk about other roles they've given their players, to split the GMing work up a little more between the players, like a cheerleader or a rules lawyer. What roles do you offer or assign your players? What roles do they often choose to take on their own?