It looks like the RPi 3 staying at 40nm lithography resulted in overheating issues for some people, this video shows a neat solution on how to quench the heat!
Raspberry Pi 3: Fan and Cooling Tests
I'd say for anyone who pushes their Pi 3 hard with Gaming, Emulation, or HD Video Watching, a heatsink & fan is highly recommended. Or at the very least, use a well ventilated case!
Here's the RPi Subreddit post of the video, with some interesting comments.