This feature is important for improving fluid-object interaction.
Display Volume
This option helps you to fine-tune fluid-object collisions, e.g. when particles go though a surface, and visualizes how RealFlow | 3ds Max "sees" an object. The helper mesh is updated when you change parameters of the "RFCollider" or "RFVolume" world-space modifier. If the collision geometry is not visible reset the scene to frame 0 or scrub the timeline.