A lot of great surmising here. Yes, I feel like it rocks the spar less to Humboldt-cut when topping but it could just be my imagination. When falling a tree uphill the Humboldt stump holds it on the hillside better. It may be that one can get a lower stump with a "traditional" notch, thus technically keeping more of the merchantable log. And low stumps do cause less grief when cat skidding or running a yarder, but the mills want the logs squared off which would mean an extra cut on every stem. Plus the grainy flair of the stump is harder on chain, not to mention getting close to the "silt-line where dirt may have splashed up on the bark of the tree. It is thought that cutting ground-level through the flare and making a "traditional notch" is overall too time-consuming to be worth the effort for a logging operation. Thus the Humboldt stump is our happy compromise. There it is in a nutshell from my experience. Having said all that, the reason I used the Humboldt in this video and all my videos is one of pride. To me a Humboldt stump is a thing of beauty. It is not upside down. The way a cutter leaves his stump is his signature. You can tell a great many things about The attitude of the tree the day it fell, and also about the man who cut it, by reading his signature-stump. Where is he from? Is he working safe? Is he hasty? Perhaps he was tired? Was the saw dull? Was he heartless and all business or was he an artist? I love reading stumps.
