these IDs do not have any impact on the simulation. They will only be important as soon as you would like to correlate the (intermediate or final) simulation results to the initial particles.
As an example: A PixelHit carries a pointer to all MCParticles that contributed to this PixelHit, which can be used to analyse the detector e.g. w.r.t. its efficiency or resolution. With no MCParticles created, this information will not be accessible.