But carrots are easier than fruit. If you go to apple or orange plantages, you'll often see the ground covered in perfectly good fruit, because it's too expensive to pick it efficiently. 20% doesn't even make it to the shop: http://www.forbes.com/sites/nadiaarumugam/2012/10/04/un-says...
In addition, being able to remove weeds mechanically, rather than chemically, is a big win for health and environment.