One point is that if someone elects to nail blazes to trees, they should use aluminum nails. Some day for some reason, long after the blaze has deteriorated, someone with a chansaw may be cutting a dead tree out of the way, and steel nails can break chains and become projectiles versus aluminum is softer and just cuts through.
As for the why of using this type of blazing, the conventional method of blazing was to scrape off the bark of the tree then paint, this exposes a lot more of the bark to disease. The current method of little or no scraping and the use of latex paint means that the blazes last for a lot less time than the old style. Probably compared to this new method, the nailed in tags last a lot longer.