I have never investigated this, but I believe that this only matters if you use the mass erosion or accumulation data available. Where the particles go is based on their diameter and material properties (i.e. momentum & gravity), so how many particles are there doesn't affect it as SW does not look at particles hitting each other, only solid surfaces.
It doesn't matter unless you are interested in accumulation or erosion rates. This is a post processing operation and it does not affect the flow field which is the assumption of LaGrangian particle tracking.