Trying to make sense of multi-farm databases

Hello all, I've noticed a change introduced to the release version in Jun 2016 that I can't find a bugzilla bug or a detailed comment for, and I wish to understand a little better: multi-farm DBs, or multi-farm BAT buffer pools if you will. Questions: * Why do we have them? * Are BAT "roles", introduced with the patch for this issue, inherently relevant only with multiple DB farms? If not, why were they introduced at the same time and with the same changeset? * Is this considered a "good idea" design-wise, or perhaps an unfortunate necessity (e.g. due to client needs)? * When you create a new DB, is there a chance more than a single DB farm will be created when you haven't specifically requested this happen? Eyal