Believe it or not, the length of your nails can also affect your body mechanics. With short nails, there is no hesitancy to use the fingers or thumb. The hand can work in a soft and relaxed fashion. With longer nails, often the therapist is concerned with scratching or hurting the client. This results in tense and less effective hand usage.
— from Body Mechanics for Manual Therapists by Barbara Frye, Fryetäg Publishing (2000)