The issue there is you have to test the product you're using to make the brownies, or whatever it is you're making. You have to know the potency in order to determine the dose you're putting into the product.
The other thing is you have to either make each individual brownie with a known amount of cannabis or have some kind of manufacturing process to ensure even distribution of the drug throughout a batch. You can't just throw cannabis on a brownie sheet, cut it up, and expect the same amount to be in each brownie. There are clear manufacturing and testing practices that have to be put in place.
Home-grow doesn't have any of that. Your home-grow person is not going to be testing the potency of their plant material, testing each individual whatever-it-is that they make. That's a crapshoot in terms of dosing.