Wolfscout - yes, loosing control during a scene, punishment or not would be bad anyway you look at it. What I am referring to is an enjoyable scene. One done to the enjoyment of both the submissive as well as the Dom. A scene can be brutal to the observer, and yet enjoyable to the submissive that is in the scene. Take canning for instance. The act of canning is quite brutal, leaving single welts upon the areas of the body that are struck. Yet to the person receiving the canning, its quite enjoyable. Now if the Dom were to use a cane in a manner that was too harsh, or were to cause bleeding from a tip impacting the body, and didn't do anything to tend to the wound. This could be perceived as abuse. Unless the submissive was seeking this type of play.
So yes, loosing control is not a good thing, and when a new dominant wants to try something, going slowly would be a wise thing. Depending on what they want to do, they might want to seek a coach of sorts.
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