If you made a cut straight through a standing log, then tipped it over, it'd pivot on the two edges and falls away before down. When you make falling cuts in a log, it pivots on the hinge. In a sense the log collapses on itself, the face creates a shortcut. In a rigging situation the shortcut creates slack in the line as the log folds. With no hinge at all, the log pivoting on the two edges, the slack would be minimal. Watch the vid again and you can see the slack in the line each time. With a winch type bollard, you can draw that slack out by pulling on the line as the log tips. You can to an extent with a fixed (no rotating) bollard too, but not as effectively. You can also reduce the slack by setting the block as close to the undercut as possible, and offsetting the face cut from the block. Does any of it matter ? Depends on the weight of your logs v the WLL of your rigging. In the video we had lots of height to play with including all the line-stretch that it afforded us, so probably not a worry. But when you start getting lower down, the chunks get heavier and you're having to stop them more suddenly, it gets a bit more serious.
The video shows the sling/block set ridiculously low. I'm not sure why they did that.
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