No. Indeed, the shoulder flip has a practical use... more than being fashionable (though some will purposely get a bigger sling to be able to do this ;))
This particular technique is useful to pull your baby closer to you, with any of the pouch sling carrying positions.
Simply, fold back the top layer at the shoulder. It will tighten the sling by about 1/2".
Just when you think you have slimmed down and need a new pouch, this works wonders ;) Just make sure that the fabric on the shoulders are holding on well and not slipping and that baby's bum is not bumping to your thighs...
In any case, if your pouch fits you nicely, you would not need to to this at all.
Then again, there might be certain positions (the hip carry, most of the time) where you prefer to have your baby closer to you.