On one hand, spherical domes have an economic and ecological surface-area-to-volume ratio. On the other hand, the kind of use as well as the surroundings require more edged contours in many cases.
In the case of a sports hall it is advantageous to round a rectangular plan.
The rows of spectator seats can follow the course of the building envelope. Besides, needless clearance that a ball doesn't pass along its round flight path can be avoided.