It's pure chemistry, it's not placebo.

THCA -> THC (decarboxylation) occurs at room temperature, but much more efficiently at hot, sub-vaporization temperatures

The efficiency of heating(activating) depends on how well the cannabis was cured and how much THCA it has before you smoke it.

The heat of the flame should cause this process to occur, but I believe it also destroys some molecules. I just can't find an article.

This is most important when making green dragon because it is the only time the cannabis is heated, whereas smoking and cooking involve heat.