I work on a small sustainable farm. We had an accidental companionship grow in our greenhouse this pst year. We were sprouting eggplant, and having some trouble with bugs eating up the babies - except for the ones that were near the sprouting holy basil (a rather pungent basil cultivar).
We ended up planting them together in the same rows. But I don’t really know if the overall health or productivity of the eggplant was better than average. Sadly, we don’t keep very good records.

One name for it is argoecology, I have practiced this for a while in my garden and several years ago experimented with it on a field scale where I planted red clover with smooth awn barley as a forage crop and peas with oats and barley. I got 2 poor forage cuts out of the red clover mix and one huge one out of the pet mix.
The principal behind this for me was to make use of the legumes fixing of nitrogen to avoid having to use any more than a small amount of N2 fertilizer. I have seen fellow NFU members in Eastern Canada use di-cott radishes, legumes(3 different types) and rye as a grazing mix that not only provides feed for animals but, allows the use of no fertilizer for either this crop or the next. They grew 110 bushel per acre corn as the next crop.
The use of deep rooted plants like di-cott radishes is an interesting one. Tap root plants bring up nutriments from deep in the soil and break down rock to liberate phosphate, micro nutriments, potassium and sulphur.
I know a lot more about the use of multiple crops being grown together some of the most interesting work in this is coming out of Africa and Cuba.

I'm a gearhead, no clue what you're talking about.

It is a great technique for gardening and for growing things for direct consumption.

I have a buddy who plants the three sisters and recommends it. I take his word for it because he has a lifetime of experience (and a PhD in botany).

I am not convinced that planting the "three sisters" is actually a sound agricultural practice. It seems to me that the corn and beans would block the sunlight to the squash, the beans and squash would rob too much of the fertilizer from the corn. To sum, I don't see how planting the three together would not result in three stunted crops due to competition...otherwise, there would be no point in weeding. It could be that the native Americans plated those three crops in close proximity, not because it was a good thing to do agriculturally, but because without plows to till the soil they used sandbars in a river that were naturally restrictive in space. Nevertheless, I am willing to learn...if someone can provide a link to a bona fide agricultural site that can attest to the wisdom of the practice, I would be very thankful.

I think the crops would be a lot less lonely being planted with a companion. The ancient Egyptians planted their pharaohs this way for their voyage to the afterlife. All kidding aside many small scale farmers already do this. Some companion planting involves plants using or producing complimentary nutrients. Others for pest control such as a sacrificial border to draw insects away or using marigolds to repel insects. Pollination can also be enhanced using these methods. Great idea, should translate into large scale crop management.

Makes a lot more sense to do it that way. My garden is small, and I've tried to plant things that are beneficial to one another.