We're not sure what causes stuttering, but something between genetics, neurology, and motor function is miscoordinated. Blocking or other avoidance are what comes from fear/embarrassment/desire not to stuttering. I'm unfamiliar with evidence that shows that. On the contrary, many have been shown breathing techniques and they don't help much of the time. There may be positive side effects but I don't know how much influence they have on stuttering.