This point is kinda hard to grok for me, but I learned it from experience. We had a backlog in a support forum, but auto-bumping one a day and a handful of attentive helpers got through it in a couple of months, until we had two threads leap-frogging each other but no one had anything to add. So we turned it off.
Now we just turn it on and off as needed, per category. 
That said, for practical use I don’t think autobump needs stepped decay, I personally think about it all time, since I also use Discourse as a personal wiki, and such a feature (say as part of the auto-timer…) would help knowledge scaffolding by providing a mechanism for Spaced repetition - Wikipedia. 