I work outside and in the colder seasons a vest is ideal because with a sweater I'll start to sweat but with a vest and tshirt I get much more airflow and the sweat dissipates easier. Plus if I get too warm it's really quick and easy to remove a vest Also I like puffy vests under my riding jacket when I ride my motorcycle because it insulates my core without adding bulk to my arms, which in an armored riding jacket the sleeves are bulky to begin with so I take what I can get