What effect does more or less kneading have on the final product?

I usually throw my proofed sponge into a bread machine and run the dough
cycle to knead in the other ingredients; adding flour and/or water to
achieve a good dough consistency. I tend to try to the dough feeling right
as quickly as possible. That's generally around 5 minutes of machine
kneading if my recipe is well planned.

On my last loaf of French bread I was experimenting with a new recipe (heavy
on sponge that was not precisely controlled for hydration)--I overshot the
flour by quite a bit, leaving me needing to add a lot of water. It took the
full 30 minute knead before I had the dough just right. The bread turned
out really good. It was much softer than usual.

Can anybody elaborate on the difference of a dough that is heavily kneaded
versus dough that is unkneaded or lightly kneaded? Was my bread softer for
reasons other than kneading?

Thanks.