I suspect that the original reason for turning it off was that it re-introduces the infamous quote button. I've
messed around with it in the messing-around forum, and I can't see any great benefit to turning it on again. I'm in favor of anything that encourages thought between reading something and replying to it -- so I guess I'd vote for returning to the status quo ante.
The Quick Reply button makes sense in a forum where "Threaded" mode, with posts and replies to those posts shown tree fashion, is an option. Since that isn't an option on TFL, the Quick Reply feature serves no real purpose that I can see, unless it make things significantly easier for someone posting from a phone. That
might be a reason for enabling it, I guess... otherwise, no.