Yes, it requires prior understanding of what you're attempting to do. That's more or less what I meant by "making your own brain work more" - if you treat it as an input for your brain to operate on and exercise your knowledge, it can boost your productivity. If you treat it as a tool that lets you think less, you end up with nothing but slop. Sometimes even slop will be useful, but the contexts where this is true are limited.

I have no doubt that agents will become meaningfully useful for some things at some point. This just hasn't really happened yet, aside of the really simple stuff perhaps.