Unless you are a power lifter who uses “gear” (squat/deadlift suit) performing maximum effort squats or dead lifts you shouldn’t need one. Lifters fill their lungs with air and force their stomachs against the belt for stability and rebound out of the lift. Many power lifters will wear belts to keep their bench shirt pulled down during the bench press. Like gloves they can be a security blanket for some people. The belt should be worn a tad loose.