"Yes I am being a azz about this because as things go here you get a drawn out answer that does not answer the question.
We all now know it works and won't hurt anything but why not just use something to stop the blade"
Because sometimes you can't hold or block the blade in a safe manner. I doubt you have ever been on a service call and don't have the right tools with you to solve a customers problem or additional request. As the OP said, "this is a tip" for the average guy. Does it take longer, YES. But as a service tech, you are asked to get the job done as quickly and safely as possible. Tips like these help everyone, except those who don't want to use them.
You asked about a deck blade. Here's another rope trick for you. Tie a rope just under the pulley and wrap it around the spindle in the opposite way about six times. Now tie the rope off on the other spindle. As you try to loosen the nut or bolt on the blade, the rope will tighten and finally stop the spindle from turning, holding it tight. This will allow you to remove the stubborn bolt.
Before you ask, yes the old mechanics who do service calls, always have a length of cotton rope in the truck. You never know when it will come in handy. Also, cheaper than having a box of single use, specialty tools.