The answer is that taut skin lets the razor cut the beard hair more cleanly. A firm, stretched surface gives the blade something even to work against.
Loose skin bunches up in front of the razor and increases the chance of nicks, while over-stretching causes irritation. Taut is the middle ground — firm enough for a clean cut, not so tight that it stresses the skin.
This is 1 of the real Shaving questions in fadejunkie's 299-question bank. See the Shaving practice questions page for a fuller sample, or try the Shaving practice quiz and flashcards for free. A one-time $15 lifetime pass unlocks the complete question bank across all 13 tested topics.
More real Shaving questions: What's the Term for How You Hold a Razor?, Which Razor Stroke Isn't Used for Facial Shaving?, What Beard Style Fills Out a Narrow Jaw?, What Does Finishing a Shave Include?, and 10 more on the Shaving practice questions page.
Browse every topic on the Practice Question Hub, or see the Texas Barber State Board Exam Guide for the full exam process — required hours, PSI scheduling, and fees.