Auto-save has been implemented for ages, and seems to work without problems.

I think the time has come to turn in on by default in 2.8. Why now? because I have answered one too many post in the quiz forum where someone was complaining about lots results.

I don't think it will cause performance problems. When we tested with 1000 simulated simultaneous users taking a quiz on a system with two web-servers, that included auto-save requests.

If anyone does hit performance problems, then can turn this setting off again.