I did it kind of half-heartedly maybe a dozen times? I did find it useful in a sense as it gave me an idea of which muscles I needed to relax. Of course on the day it feels completely different, but it may have helped. Had a 6 hour labour with ARM and synto, no stitches, no tears or grazes. Although as the others said I also didn't get any stretch marks so maybe I just have stretchy skin (although now I have stretch marks on my BBs cause they have gone from a B to an E ). The midwife thought I would need an episiotomy but my OB bless him, never mentioned it or appeared to even consider it.
GL!