The other benefit is that it prevents a stronger temperature swing in the freezer/keggerator. If you have a 5 gallons of fermenting/cold-crashing beer, it'll have a very high temperature inertia. The freezer will over compensate to lower that mass (especially if you're like me and use a thermowell), which may very well result in your temperatures hitting the low 20's / high teens. This is mitigated somewhat by using a smaller vessel (i.e. paper towel taped over the probe to attach it to a can of beer), but that doesn't tell you what your wort is actually doing. I've inadvertantly froze wort this way.