(= spend resources) when there's no-one to see the particles
How is that there is no one to see the particles? In his example, he has the particles attached to the player itself. And once the player moves away certain distance of his original position (where the particle source vehicle was created), the particles surrounding him dissapear.
The problem is the followin. Particles may get absolute positions or positions relative to objects. And, of course, particles generated by particle-source vehicles may be attached to objects, so, their coordinates will be always relative to that object (for example, the player).
You may create a particle source vehicle and start generating smoke, using just the absolute coordinates of the particle source vehicle. In this case, it may make sense to only generate particles with coordinates close to the particle source vehicle, because it is placed in the origin of the smoke. But, if the particles generated by the particle source are attached to another moving object, for example the smoke trail of a jet, it is quite possible that this object will move fast and well away of the particle source vehicle, and the particles should keep there because they are, in fact, attached to an object different than the particle source itself. This is what is not considered by the current commands, hence the bug.