Tilling and fertilizing gives you a great yield today, but damages the long term fertility of the land, and pollutes nearby waterways. The best analogy is buying things on credit. You might feel rich at first, but when the debt comes due and you can't afford it bankruptcy is a bitch.

It does require letting some land lie fallow to regeneration, so you need to devote more total land to agriculture, and it also requires fencing and for someone to go move the livestock to a new paddock every few days (though you save on tilling/herbicide application costs). On the plus side the unit cost of everything you produce is lower, and meat is typically much more profitable than vegetables so you've diversified.