I think I agree with your general point, that burning STEEM/SBD isn't necessarily good for the economy, because if there's nothing exchanged for the burn, then it implies a value of zero for the token. That had never occurred to me before you mentioned it in previous comments, but I think it seems right.

In the case of "post promotion", however, whether by sending SBDs to @null or by setting the beneficiary to @null, I think this represents an exchange of value so that it increases utility for the tokens and also produces more of a "circular economy", so (as long as its voluntary), I do think it's a good idea to encourage experimentation.

Also, as I noted in my post, I think that Tron's recent price performance makes a pretty compelling case for burning tokens when it's done in exchange for a service.