[Suppafly]

>Now I wonder how much of it is true and how much is romanticizing an idea that is a meme and sounds good.

I've long assumed that that's what is happening. Also, you can't just throw all three seeds in a hole and call it done, you have to start the corn and then later start the squash and then later start the beans. It's a whole process. It probably works in specific conditions, but in general normal yearly crop rotation to replenish nutrients with things grown in correctly spaced rows and such is likely to work better and be more labor efficient.