I was brought here my @curie! Yes, many weeds are nutritious, and most greenery normally hauled off-site would still probably serve better as compost so the nutrients can return to the soil.
That said, we have a few truly noxious weeds here which warrant special attention. Spotted knapweed is an abomination! You can't eat it, livestock can't eat it, it poisons the soil, and happily grows in gravel.