Mark makes an important point. Finding the queen is important for the reasons he mentions, as well as indicating whether reversal of brood chambers is warranted. As Mark says, the normal progression is that the lower box fills up, and she moves up. After the brood in the lower chamber emerges, if there is no room, the colony may begin storing nectar and pollen in the now open cells. THis further congests the brood chamber and the colony may become "honey bound" often leading to swarming, reduced production, etc. If by chance, she has moved down on her own, reversing the boxes puts her back on top and again, out of laying room. Integrity of the brood chamber is an important factor too. If you were to find the lower brood chamber full of honey, with the outside frames undrawn, some frame manipulation may be warranted to get this back in the right shape.
I've read alot of different theories abouts swarms. Some think it is the natural reproductive plan for the honey bee. Some claim that it doesn't happen during a flow, and it is an attempt to find more forageable territory as flows end. Most agree that brood chamber congestion is a factor. In any case, with mediums, 3 hive bodys is not unreasonable as the colony expands.
I think that we all need to learn what is happening in our environment, in regards nectar flows, heat/cold, our bees' propensity for swarming, etc to become good managers.