Probably to check the load and quick check tires and lights.
In hauling cattle and horses, most drivers will load, rearrange gear used and in cab preparing to hit the road. Then drive away a few miles to an open spot; preferably lighted, but vacant and room to walk all way round.
Stop, get out and walk slowly around the rig, peering thru the backlighted slats for any lying down already. You see only legs, all is up. They have in this short distance somewhat accustomed themselves to the shifting movements. Do not have to use a flashlight to inspect. As you walk around, you see any clearance lights not burning and can "kick the tires"
with foot or tap with a hammer. Vacant and open is to be reasonably safe from any mugging and if animal is down, you can shock with your hotshot in privacy. So many people take a stick stuck horizontally in as you beating the animal.
I have hauled a lot of cattle, WI to Miami, FL. This is cattle.
Hogs were usually large top hogs (230 to 250 lbs) and E. St Louis to packers on south. Sensible number loaded will have adequate room to shuffle together and no problem of down and trampled.
I never hauled these little pigs;or short distances, but feel the comparison is reasonable.