 How does the shape of Starre's ship benefit them?
Moments later, they were outside the ship, with star-powdered infinity spread to all sides. And yet, if by some chance there was such a rigidly specified asteroid, their financial worries would be over. Now that he and Queazy had found the asteroid, they were desperate to get it to its destination, for fear that the Saylor brothers might get wind of what was going on, and try to beat them out of their profits. Now they scuffed along the smooth-plane topside of the asteroid, the magnets in their shoes keeping them from stepping off into space. He satisfied himself as to the exterior of the asteroid, and then sent the twin beams deep into its heart. He and Queazy caught up with her on the side of the asteroid they hadn't yet examined. "You want to move this asteroid from its orbit and haul it back to Earth. About twenty steps away was her small dumbbell-shaped ship, so shiny and unscarred that it reflected starlight in highlights from its curved surface. A few hundred feet away, floating gently toward the asteroid, came another ship—a ship a trifle bigger than their own. "It's—it's very important that this—this asteroid stay right where it is," she said huskily. The big ship had landed, and little blue sparks crackled between the hull and the asteroid as the magnetic clamps took hold. A few seconds later, the airlocks swung down, and five men let themselves down to the asteroid's surface and stood surveying the three who faced them.
 Being a "yo-yo" shape, they can use it like one to fight against the Saylor brothers.
 It made it easy to spot and to re-locate it.  It's small, making it easy for them to transport it with them.  Being a "yo-yo" shape, it was easy to attach cables to it and maneuver it back and forth.  Being a "yo-yo" shape, they can use it like one to fight against the Saylor brothers.