Oh and P.S. if this isn't a multiple choice question then I would like to put my answer. I believe that the reason you have to cut your hair, fingernails, and grass is because all of these things if left uncut will continue to grow and leaving them long can negatively affect the health of said hair, fingernails, or grass. also once someone cuts said hair, fingernails, and or grass then these things will begin to grow faster. Hope I helped!