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This parameter adds extra particles around the simulated particles. The simulated This way, a lighter simulation with a small amount of particles can produce a more dense cloud by multiplying them at render time. The new particles are affected by the speed of the original ones, so your particles must have some velocity as the extra particles will be scattered based on the trajectory of the simulated particles. So if your particles aren't moving, this parameter will not change anythingor this parameter won't have any influence. Note that more RAM will not be used if you create extra particles, this depends again on the final number of cells created by the cell size parameter. If you do use a high dispersion though, it is likely that many more cells will be created since the total bounding box of the particle cloud will increase, thus increasing the amount of RAM needed for rendering.
Extra particles dispersion
The distance (in meters) that the extra particles should be allowed to disperse from be randomly distributed around a sphere based on the original position of their "parent" particle.
Extra particles deformation
This has the effect of exaggerating the motion blur shown on the extra particles, making them move faster than their "parent" particleThe new particles can be generated randomly inside a sphere based on the position of the "parent" particle, or inside an ellipsoid with this value of eccentricity. The ellipsoid is aligned along the direction of the parent particles speed.
Motion blur factor
You can control the amount of motion blur visible on the particles, separately from the scenes main motion blur settings. If you want the particles to look blurrier as they move, increase this parameter.
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