Tip plates work well to reduce induced drag at lift coefficients of over 0.5, but they increase total drag at lower lift coefficients, and are seldom used now, except in the form of NASA winglets. I have experimented quite a bit with them on a competition fun-fly airplane, and found that they reduce aileron yaw, due to the additional yaw resistance supplied by their additional lateral area up forward, and help extend good lateral control deeper into stall territory. They also result in a smaller minimum turning radius, due to the reduction of induced drag at high lift coefficients, but hurt top speed a bit.