A two-piece wetsuit provides you with more flexibility in movement compared to a one-piece suit because it allows for a more personalized fit. With a two-piece suit, you can select a top and bottom that best suit your body shape and size, leading to a more comfortable swimming experience. As for buoyancy, it depends on the wetsuit thickness. If one piece of your two-piece wetsuit is thinner, compared to a one-piece wetsuit that is uniformly thick throughout, then of course the two-piece would provide less buoyancy.