#farming
Subsistence farmers generally do not do this. Remember, the goal is not to maximize profit, but to avoid family destruction through starvation. If you only farm one crop (the best' one) and you get too little rain or too much, or the temperature is wrong that crop fails and the family starves. But if you farm several different crops, that mitigates the risk of any particular crop failing due to climate conditions, or blight (for the Romans, the standard combination seems to have been a mix of wheat, barley and beans, often with grapes or olives besides; there might also be a small garden space.