Yeah, the slope on half the orchard is approaching 45 degrees, maybe steeper in some areas. Makes for a long ways down on the one side of the tree. Most of the trees are 50 feet tall and taller- where the trunk meets the roots.
Grafting is really just ancient genetic engineering. I grow some 'root stock" from seeds (chestnuts), but those trees are not going to produce identical fruits to the tree that bore the nuts I sprouted from. They will be a mix of the two trees that parented the seed. One being the "mother" tree (the one that bore the nuts- or "eggs") and the "father" tree- the one that pollinated (or fertilized) the female flowers that produced the nuts. Chestnuts are not self pollinating for the most part, you need two trees to produce nuts.
Now, in order to get the exact same nuts that I get from the tree that I took the seed from, I graft the seedlings with scion wood from that same mother tree, using the seedling as root stock. The nuts that are produced from that graft are clones of the original tree. Now, to make a tree self-pollinating I will keep half of the branches from the original tree, and half will be grafted. This will produce a mixed crop, but there is the chance that the seed stock has improved upon the mother tree I took the scion wood from.
Pretty much the same thing for any other plant. The only way to get an exact duplicate is to grow from a cutting or graft on scion wood from a know desirable tree or other plant.
The above described process is what was done with avocados back in the 1920's. A postman named Rudolph Hass ordered a seedling from a seed company, which grew into the best avocado the world had seen, and since then. He was an amateur horticulturist and started grafting from his tree and selling the grafted plants, which are clones of his tree. That is where the Hass avocado came from. Its an interesting story.
Walnuts typically will be grafted for a superior rootstock (typically black walnut) to be married with a high yield and flavorful nut producer- like the English walnut. This is why the trunks look really rough and deeply crevassed and then there is a distinctive line where the tree turns very smooth and white bark.
You can build Cornucopia trees that have different fruits or nuts (though you have to stay roughly within the same family)- I have seen nectarines, peaches, plums and almonds on the same tree. or avocados and oranges (this is extremely rare I am told as it is difficult to be successful with it- though they are both citrus). Roses can be grafted to produce many different color flowers from the same trunk.
Hope this helps!