The decline payout option seems like a mere band-aid though; can't imagine many whales voluntarily making use of this, but I guess we'll see.
The main purpose for this is so that when @dantheman, @ned, etc. create posts that are official Steemit communication, that they don't take from the reward pool when the post gets a lot of votes. Some witnesses may use it to if they feel that their efforts are getting sufficiently rewarded through witnesses pay, and don't need to double dip and also get paid through their post.
It is possible that some altruistic whales might choose to do it too, but I agree tthat this probably won't happen very often.
Yeah, that makes sense. I guess the whole "with great power comes great responsibility" thing comes into play here. Let's hope the Powers That Be use it wisely!