This EditMode helps in creating Particle systems on the map. These can be used to simulate effects like fire, smoke and many more.
To create a Particle System, just click on the grid when this EditMode is active. This will create an “empty” particle system, meaning it is just a container and no real particles are shown (yet) Optionally, there are two parameters one can set up prior to placing Particle Systems on maps. These are:
Have into account that these options will be valid for objects created right after changing them, so any Particle System that is already created will keep its settings.
More on Particle Systems here.