not at all, this discussion has been debated many a time. As far as I am aware no one really knows 100%, everyone has there own opinion. I wouldn't worry about it losing gains per say, some people will say that doing it directly after a workout may undermine it a bit. Use the search function because there is countless stuff on it. I think its more a preference thing, I try not to because my penis tends to retract (turtle) abit have masturbation, especially if I have just done a girth workout as I tend to lose some pump as I'm no longer in a sexual state of mind. That said, if I happens, I don't lose any sleep over it.