Loading heavy material on a sloped surface should generally be avoided because it:

Loading heavy material on a sloped surface can significantly increase the risk of accidents and equipment damage. When operating heavy equipment like a tractor-loader-backhoe, the stability of the machine is crucial. Slopes can create an unstable environment, leading to tipping or sliding, especially when heavy loads are involved. If the center of gravity of the equipment shifts due to the incline, it heightens the likelihood of losing control. Furthermore, the added strain from loading on a slope can also lead to mechanical failure and increased wear and tear on the equipment.

On flat surfaces, operators have greater control and stability, allowing for safer and more efficient loading. Therefore, while loading on a slope might seem like it could be faster or easier in some situations, the potential hazards make it a practice to avoid whenever possible.