On older hardware it makes a huge difference. Also very useful if you are on a battery, in my experience it can be the difference between 2 hours or 6 hours of battery life. I think it's off by default because hardware acceleration sometimes introduces visual artifacts but these are so minor I would prefer the extra 4 hours of battery life and not giving a hot laptop. YMMV and indeed it may not be noticeable on newer hardware and maybe not an issue if there are no batteries.