Visibility was one. At the time the top slot only cost about 20 cents. He overpaid. So that was pointless. A waste of money and resources. He also said it was a tip. So, let's say he tipped me 3 dollars. He wasted his money using a middleman. He could have sent me that 3 dollars directly. Instead, a middle man also earns 3 dollars because that's what the vote cost PLUS the bot earns curation rewards, meaning I got shortchanged on my so called TIP.
That's true unless someone feels that bot services are beneficial to the STEEM economy, in which case it's more efficient to use one to boost a comment because then you can give to the bot owners/delegators and to you at the same time. From which perspective there is essentially zero waste (not including the "stealing from the rewards pool" argument, which, again, I find quite spurious) because you're being rewarded for the comment, and the bots/bot-owners/delegators for their service. It also increases your reputation number very slightly, as you know (and also know that it doesn't mean too much. Thus: @steem-ua.)
If, however, he's just wanting to give you a gift, it would be more efficient to send to you directly, I agree. Renting delegations to have greater influence on allocating the rewards pool is also a decent option, and much more accessible to those of us that don't have six figures sitting around to pump into buying SP.