What the gluten look like when kneading for long time on a texture basis
Kneading gives elasticity and strength to your dough. I'm not 100% sure about pizza dough, but a brioche dough requires quite a lot of kneading, to allow for the air created by the yeast during proofing to stretch it. If it's not kneaded, it wont be able to stretch enough, and will be rather flat and dense when baked.

Most doughs are usually rested at cold temperature, and rolled out later. And in the case of brioche, you actually knead it some more while rolling it.