Beyond the traditional explanation of what smoking does to hives (fools the bees into thinking there is a fire and so they are busy consuming honey, and the masking of the alarm pheromones) there are other considerations of what smoke does.
Have you ever heard someone say they smoke with tobacco, walnut leaves, sumac pods, or some other material and suggest that this somehow kills mites right off the backs of bees? Or how about the crowd that suggests that nothing good can come about by smoking bees and that it's cruel to the bees? I think there is something to consider on both ends of the spectrum.
Killing mites by smoking them:
I have used just about everything suggested. And I smoke the crap out of my bees when testing a material. I have found nothing that will kill mites off the bodies of bees. And if you are killing mites off bees, your probably doing damage to the bees.
Here is something to consider. Smoke your hand or wrist this morning. Smoke it real good. I bet, unless you wash your hands, you will be able to smell the residue from the smoke this evening. And it's this residue that is in conflict with the bees natural smell, pheromones from the queen, and interferes with the communications of the hive, which much is controlled by smell.
So what do the bees do? They go into a hyper active period of cleaning, grooming, ridding themselves of this left behind smoke residue. This is when mites are groomed at an increased level and an increase in mite drop can be seen. (This action can be also seen and proved in studies, that merely opening a hive, with no smoke used, and doing a brief inspection will cause bees to groom and "correct" any disturbances within the hive.) I will not argue that mites are not jumping off if they smell smoke...as it probably has not been studied and many insects react to fire or smoke in different ways. But certainly they are not being killed off the backs of bees, and since a spike in mite fall can be seen for up to 24 hours after a good smoking, one could only assume that bees are still grooming mites off long after the mites are done taking any notion of suicidal jumps to their death.
Smoking is cruel to bees:
If one thinks of the benefits to bees from the above comments, and the lessening of the mite load, I can see no cruelty from smoking bees. This same benefit of smoking is seen from those that use sprays with thymol, etc. However it should be noted that for the best results in mite drop on an occasional basis, that long term exposure to these smells should be avoided. (Laced patties, etc.)
Obviously bees that are hygienic, are great groomer, and deal with mites on a constant basis is a good thing. But blasting them with a good smoke that triggers some hyper house cleaning activity is not a bad thing to consider.
Just some random thoughts this morning..... :-D