Road construction and clearing and grubbing have been something we humans have been doing for thousands of years. The very first time humans started clearing land was to grow their food. This led to them having to build tools. The tools were too heavy to carry so they needed a place to be stored, the humans, now no longer travellers needed a place to sleep as well. Humanity cleared land because they wanted to stay there, forever. This process of clearing land is still used today and while the tools have changed the basic concept has stayed the same. The goal in clearing land is not just to get rid of trees, cutting a tree down still leaves a stump. To farm or build on the land without issues that stump must be removed. So must any detritus, fallen branches or trees. Weeds, bushes and even the very roots of the plants. Have you ever seen a plant growing through concrete? The crack was not there before, the area was not properly cleared and seed or plant was left. Plantlife is highly tenacious and aggressive and is still stronger than most of our building material in that they can outlast them. So if a small plant can grow through a concrete slab of sidewalk, creating a crack in the process imagine what a tree seed like an acorn could do to your home in twenty years. It could grow through your basement floor, destroying the foundation of your house entirely and causing severe flooding in even light rain. This is why clearing and grubbing are so specific. Everything including the first layer of topsoil must be removed everywhere. Roots must be dug up and stumps can just be cut out of the ground you must retrieve every single root. If not then years later someone in the planned community you built long ago now has a bush growing through their driveway or a tree breaking through their basement.
There are numerous instances of clearing and grubbing that need to be planned for. Even placing a natural item like a tree or a bush too close to where the structure is built could, in time damage the structure. That is the purpose of clearing and grubbing. To prevent long-term damage to roads building and other structures from tiny remnants of plants that are still alive. A tiny strip of dandelion root left in the ground after removal will result in thousands of dandelions popping up next season.
To properly clear and grub areas is to excavate them. Remove not just all of the plant matter, rocks, grasses and shrubs but also excavate the dirt. In residential situations, this often needs to be done down to a distance of a minimum of 8 feet. In road construction, it is 70 to 100 feet that must be excavated as the danger of a highway or skyscraper cracking from plant growth is far more dangerous than a residential house being damaged by plant growth which is also a far more common incident.