Honestly, this genre of "Look! We don't do X!" topics on HN recently have been a little absurd. Advertising has it's place. If you're buying ads on your own brand name then yes, you're wasting your time, but since advertising is quite expensive I would've thought you would put some effort into doing it well. It's the same thing for the unit testing article and the article about staging environments. Yes, if you do something badly, it's probably going to be worse/more expensive/slower than not doing it at all. But the whole genre could be concisely summarised as "Be concious of where you are focusing your efforts".
If you don’t buy ads in your brand name your competitor might and May encourage users to try them instead. Even if you lose 5% each time, that can build up.
Companies do this all the time. Even for something like App Store submissions. People use their competitor name as a keyword to increase their top of funnel.
I'm sure it happens, but you've got to be looking at that as a pure cost. You're not generating any revenue from people searching your brand, and you're paying significant sums for click through on people who already had the intention to come to you. In some ways I could see the normal position being "We only advertise on our competitors brands" because atleast that way you are picking off your competition, not bidding up people who already wanted to come to you.
