It's what I was taught years ago, but as a hypothesis it wouldn't appear to offer much in answer to the obvious questions. For example, if it were to suggest to the bees that their nest was at risk of being burnt down, why would the smoke have the effect of calming them? It's argued that bees can't sting when their crop is full of honey, but is there any evidence for that? It wouldn't really be a very well evolved response to predators would it, if half their flying time when they're collecting nectar or water they're defenceless? And what about all the bees that can't sting anyhow -- the nurse bees and drones, for example? What will they be doing? If the effect of smoking the bees is to get them all to stuff themselves with honey so they can leave, wouldn't you expect them all to be madly rushing about when you open up the hive rather than calm and easy to work with? And if it's true, as I was also taught, that prior to swarming the current queen is slimmed down in order to fly, what chance does she have of flying sufficient distance to escape a fire when she isn't? And if they're going to leave, what actually triggers that? Is it common for colonies to abscond during inspections when the beekeeper overdoes the smoke? I'm sure I was as cack-handed as many when I started out (sometimes I still am when my brain isn't properly in gear) and it's never happened to me.
I know it's also suggested that smoke "disguises" the alarm pheromones, but I'm not entirely convinced by that without further evidence either. My understanding is that bees have specific receptors on their antennae for sensing pheromones so why would they not still be able to recognise them?
It appears that bees don't like smoke though and will try to move away from it if possible. These days that's pretty much the only way I use it: to try to persuade them to move away from an area I'd like them not to be -- all over the top bars of the brood chamber when I'm opening up the hive to do an inspection, for example. I don't puff smoke around the entrance of the hive (as I was also taught to do) before opening up or anything like that. I can't see what it would achieve other than potentially agitating the bees, though I suspect it does very little at all other than perhaps make the bees very close to the entrance withdraw a little into the hive.
James