Nate, I too many times will cut high but usually go back after the tree is bucked and cut that stump down.
Whoever was cutting was probably dropping multiple trees by creating the partial cuts and then dropping one larger one on all of them - no center fiber pull, which is lost board foot in lumber logging.
A couple of reasons for the Humboldt cut. 1 - Cleaner end for logging, 2 -It encourages the trunk to slide off the front of the stump vs sliding backwards over the stump. Thus decreasing the risk of it jumping back at the saw operator. This risk is why the saw operator will normally find a retreat path at a 45° rearward for safety. I kneel when making my notches so the stump is not near as tall as what you see in the drawing. If you are cutting on a hillside where you want the tree to fall down hill, there is very little stump. As to the depth of the notch, where I came from in Northern Minnesota, there was a lot of pulp wood being cut. Most of it grew fairly straight up. With this type of tree, where only a little bit of persuasion is needed to direct the fall, it wasn't uncommon for the notch depth to be 40-50% of the trunk. It made it very easy/fast to tip the tree rather than have to lift more of the tree with the wedges to get it to tip. So depending on the tree's natural tendency to fall whether from lean, limp weight/pull, & wind, I will very the notch depth accordingly.
Kinda wish I had his PPE on the other day when cutting a 1.5" piece of PVC on my pool piping - stuff gets a bit brittle over the years and ratcheting cutters create pvc shards/bullets, glanced off my forehead...no boo-boo that needed 2 stitches
