[yamtaddle]

I could see "it does nothing for you" for some set of things, but it cannot possibly be absolutely true. For one thing, stretching has been very successful in increasing my range of motion. It may be, however, that it e.g. doesn't do much for reducing, say, back pain or improving overall health outcomes

It clearly does something, but it's possible that in the context of the claim it does indeed do "nothing" (nothing, or so close to nothing that it might as well be nothing, to affect the specific things in question)