Any kind of session is good for stress as it creates a more immediate stress. Being flogged puts stress on you as in pain, possibly embarrassment (depending on the condition), discomfort. This stress overrides all other stresses going on. When this stress stops, and the endorphins are flowing, all other stresses go away as well.
This is why I love this. I do and teach meditation, and it is good for stress, and keeping stress away. But if one is stressed, it is hard to get down and meditate.
Flogging immediately takes your attention away from your problems by giving you new, immediate problems. Once it is over, the other problems while not going away permanently, weigh a lot less on you.