Drag resistance training is an important part of swim training. It helps improve muscle strength and endurance. The use of equipment such as sleds, vests, parachutes or bungee cords is common but so is something as simple as a drag suit. When I was swimming we would layer old suits. Wear t-shirts under our speedos. And even old blue jeans. Unless you are feeling really adventuresome there is no need to go to such extremes. While drag suits have been shown to affect some swimmers' stroke distance, using drag suits for sets that incorporate periods of rest which allow swimmers to maintain proper technique can be beneficial.