Rapid Clear (flocculent) basically makes unwanted particles larger. Normally when green water/ dirty water is present in the pond particles are negatively charged and repel each other, by adding Rapid Clear or flocculent (polymers which are positively charged) the dirt and debris will attract to the polymer and form a larger structure. In the case of a Rapid Clear the particles or turbidity can now be mechanically filtered out by your filter system or drops to the bottom of the pond and your water becomes clear. If you initially overdose Rapid Clear it can cause a reverse negative charge that will repel debris from other debris. You can definitely do multiple applications just leave at least 12 hours between dosing as a basic rule of thumb.
Use of Rapid Clear, with a Rapid Clear Fine Filter Pad will remove the dirt or debris rather than letting it degrade in the bottom of the pond and re-release nutrients. Strong aeration also makes a huge difference when using a flocculent, it keeps all the debris and suspension so it can be removed by mechanical filtration but doesn’t chop up the flocked debris like a pump.