MassFX Flow creates a simple Particle Flow setup that is wired for MassFX simulation; just play the animation to see the physics simulation.
The global PF Source event has the Quantity Multiplier settings for both Viewport and Render set to 100% and Integration Step for both Viewport and Render set to Half Frame. This is done to have the same amount of particles in render and viewport; and have the same integration step, thus ensuring that the rendered simulation works the same as the viewport simulation.
The Shape operator is set to the Cube type, with its Size value slightly smaller than the Grid Size setting in the Birth Grid operator. This prevents particles from colliding at the moment the simulation starts.
The Spin operator has a low Spin Rate value to create a random small spin for all particles. This enhances the simulation effect, because particles move slightly differently from one another and do not copy or clone each other in their relative motion.
In addition to the MassFX World operator, the preset creates a MassFX World helper (the simulation driver) and associates the two. The MassFX World helper has both gravity and the floor (Ground Collision Plane) enabled, and is positioned at Z=0.0.