[Serious] Why defecation?

[John 6IX Breezy]

And from the ground. A non-sessile plant could do better, moving when the resources were depleted.

My assumption would be that a plant which moves requires more (or different) nutrients than a plant which doesn't. Because organisms use what they use, in order to be what they are, and do what they do. Thus why a plant is constrained in its form by it's use of solar energy and we aren't.

Waste exists because there aren't deposits of pure carbon or glucose around. Nutrients are found alongside other substances. And it makes sense for digestive system to parse apart food, keep what it needs, and leave behind what it doesn't.

Perhaps a better criticisms would be why God didn't put easily accessible deposits of every nutrient around. But then again, it seems easier to just eat a fruit with potassium, than to go hunt for potassium, sodium and glucose deposits individually. Not to mention the dose in just a spoonful of something like potassium probably far exceeds your needs anyway (I don't actually know).

Eating a fruit and discarding what's not needed seems far more reasonable to me.