A common myth: when you add the stencil ink onto your string bed, the quality of the string is lowered which is why professionals dont stencil during training to make the string last longer. I have not experienced this as the string lasts as long as it does regularly with the string not stenciled. Since the string is coated with some special polymer, how could the ink penetrate through?
They probably don't stencil in practice because 1. Nobody is watching so sponsors don't care. And 2. The string is going to break so soon it isn't worth their time Also if there was a performance issue then wouldn't they want to always practice with the same stencil as they would use in tournaments, so that as many factors as possible remain constant?
Sponsored players have their rackets strung for free most of the time. It's probably just wasted money and time to stencil the rackets during training.
