Someone just did a thread, with video & stuff: https://www.mopedarmy.com/forums/discuss/7/188428/188428/
Bottom line: reeds help with throttle response, especially low-midrange rpms. Good ones can help you get away with a carb that's too big. They also minimize blowback. Top-end flutter minimizes their value unless you get real stiff ones (carbon-fiber, etc.), but then you might lose some bottom-end.