I'm a gamer, and when I play games performance degrades over the course of a day. I have no idea what the cause is.
Rebooting instantly solves the problem. I can reboot fairly quickly since I keep my system relatively clean to improve performance, so if I'm playing a game and my performance is low, I can quit out of it, reboot and rejoin it quickly and almost double my performance sometimes. This is very frustrating as I'd like to maintain this high performance at all times and not have to bother with rebooting.
You'd think if it was bad memory management on the part of the application simply closing it and starting a new session would be sufficient with no need for a reboot, right?