The noise constraint allows to use a usual Cinema 4D 3D noise to drive other nodes.
This is a great choice to modulate emissions of grid data but also particles (e.g. black noise values would not let an emitter generate particles) or forces.

As all the settings are known from Cinema 4D we refer you to the C4D help and the Noise channel shader page (...XSLANOISE.html) and will not list a description of the settings in here (no need to reinvent the wheel argument ;).If results are mapped, this spline curve defines the new mapping.