Pro Can be nadired / under supered
The space in the hive can be increased by nadiring (i.e. adding new boxes under existing boxes as the existing boxes fill). This means less empty space in the hive, making it more thermally efficient (and thus simpler for the bees to control temperature / more likely to survive the more extreme temperatures).
Pro Honey is stored above the brood
The honey provides an insulating layer which aids the hive's temperature regulation.
Outside of equatorial regions, the brood naturally moves upwards into the honey supply during winter feeding. Thus having the honey above the brood avoids bees not finding their honey supply and starving during winter.
Pro Easy to build
Instead of purchasing one, it's fairly simple to build your own at a fraction of the cost. Instructions are freely available online: