One feature I miss from reddit is preventing my inbox from being cluttered by responses to comments that I don't care to read.

Seems to me that any comment that goes about +50 inevitably attracts commentors that are better off ignored. The inability to turn off inbox replies for a controversial but upvoted comment results in spam that reduces incentive to participate in the community.

Me personally, I find negative comments easier to respond correctly to when they're presented in the context of the other comments as opposed to isolated in my inbox.

As such I believe this feature contributes to higher quality participation overall.