The @commentrewarder bot is really useful once you understand exactly how it works... in this case, I am mostly speaking to the potential for abuse.

The original poster is actually in charge of where the comment rewards go... it's not just automated. If I don't upvote a comment, it gets nothing. I might upvote a great comment with 50% or even 100%, a fair comment with 20% and a "barely qualifies" comment with 5%, and the bot allocates the amount to be distributed accordingly.

As much as anything, it was developed to help relatively new publishers with lower HivePower reward worthy comments. So if I only had 500 HP, and still voted according to the pattern outlined above the part allocated from the post rewards would be distributed the same... thereby bypassing the infamous "dust threshold."