@adrianN: You are talking about what is called marginal land in agriculture and environmental science. Recent research shows that even marginal land has a better GHG balance when left untouched and not grazed by livestock

It's always better plant and eat the food directly than to feed it to an animal.

Of course, if you're in a scenario where you live on a small island with no connection to the outside world, and you only have marginal land, yes, you need might need to have livestock to survive. But that's not what we're talking about here.