Particles may have a little gain, since they are never rotated for exemple (which can be a real issue for some uses) and that expressions for each single particles don t exist (but since the particle object itself has them, that is irrelevant), but the gain should not be that big of a deal and seems more like a habit rather than a justified choice (that may be for an easier time replacing objects with the replace object functionnality).
If someone has to go that far just for performances, I would suspect that is a micro optimisation, for me the awnser is more "it is a science curiosity question, not a question that would be useful"
Also not checking collisions won t check them magically, so that is not an explanation I think.