> For what purpose?

To understand, same reason you reverse engineer anything. Doesn't have to have a further goal than that, understanding the brain better helps in so many ways. But like most technology, obviously can be used for bad too. Should we just skip researching some topics then?

We have a good understanding of the function (and more importantly dysfunction of) kidneys, lungs, heart, etc. from high level to cellular level.

For brain, our understanding is fuzzy, more like "this part is important for that behavior" or "here is how neuron works" but we don't have a holistic understanding.

If we had that, we could more easily diagnose and treat neurological disorder.

I imagine a good model of the brain would contribute enormously to alleviating psychiatric/mental health disorders.

To do human brain activities at scale.