Let livestock eat off grass without destroying the tile.
Maybe require X tiles of grass for every animal within a pen.
If an animal is eating off grass they won't
breed
gain any benefit from eating hq food (equivalent to eating q10 fodder)
produce wool/milk
Lets people take long breaks without having their farms decimated, lets people who have cows for pulling carts go and do non-farming stuff.
realism...
Edit => added jackards suggestion