I wear one every day, my main reasons have been: 1. When I wear a white shirt i dont want ppl to be able to see under it (modesty I guess) 2. When working I commonly have my shirt un tucked (so I dont have to worry about tucking it in constantly). Also I have a fondness for big belt buckles, so it helps me keep from getting buckle rash, and there isnt a plumbers crack showing when I bend over. 3. They actualy DO help soak up sweat. 4. T-Shirts just feel constricting under a button up shirt... Something about the sleeves... it irritates me (I have OCD by the way) 5. I believe they look better under a button up... I dont like undershirts showing.. there is a reason they are called "under shirts" yaknow.