There are lots of ways to do Harness Engineering well and poorly, but the most important one comes down to whether or not you're practicing Bitter Lesson Engineering.
Bitter Lesson Engineering is my take on Prompt/Context/Harness engineering that comes from Richard Sutton's "Bitter Lesson" blog post from 2019. It means ensuring that you're not trying to outsmart your own AI. And specifically, not trying to micromanage how your AI does things, but rather specifying what you want done.
In other words:
Bad Harness Engineering is bad because the smarter AI gets the more antiquated your instructions will become. And at some point (maybe even now?) they'll make your AI stupider instead of smarter.
Good Harness Engineering is good because no matter how smart an AI becomes it will still be better at getting you great results if it understands who you are and what you like.
Basically, both your prompts and your harness should be about who you are and what you're trying to accomplish, and not specifically how to get there. That's what the AI is there to figure out.
Give it the best possible picture of you, your ideal outcome, and the best tools you can, and give it room to work.