Their main function is to keep Ha'tak vessels under construction above the ground until they are fully built and operational. They usually encompass the Ha'tak vessel itself. There are around six platforms that help the ships levitate. However, they are in a state of balance, and if one platform is disabled or shut down, the rest of the system would be unable to compensate, and the vessel will plummet to the surface. (SG1: "Orpheus")