In the farm case, you can always drive forward. It was part of the engineering of the workflow for that operation; for every operation, there is a forward path to completion. You don't have to chose between anything, you just have to know that you can't drive backwards.

Comparing the risk of parking a car backward into a parking spot and backing a large truck with no rear windows is apples to oranges. But if we must compare, the risk of damage is much higher with a truck that can back over a small car with little effort, when you are in the middle of a field you don't expect anyone to be there, like in a parking lot. But people do drive out into the middle of a field in a little pickup to deliver that case of oil or a sandwich or fuel up your truck or combine. (Sidebar, it's not uncommon to bring a fuel truck along side another truck or machinery and fuel it in motion). During harvest, the work day is usually 16+ hours which doesn't include breakfast or dinner and from the start of harvest to the end there are no days off unless it's raining. Add to that that driving in circles for 16 hours a day is a very boring job. Also note that many old grain trucks have poor breaks or breaks that are overloaded when filled. Needing to drive backwards implies that you've pulled the nose of the truck into something of value then used your breaks to stop before you hit it. Given all that and the space that you find around most farms, why would you risk driving backwards?