Sacred Harp singers view their tradition as a participatory one, not a passive one. Those who gather for a singing sing for themselves and for each other, and not for an audience. This can be seen in several aspects of the tradition.
First, the seating arrangement (four parts in a square, facing each other) is clearly intended for the singers, not for external listeners. Non-singers are always welcome to attend a singing, but typically they sit among the singers in the back rows of the tenor section, rather than in a designated separate audience location.
The leader, being equidistant from all sections, in principle hears the best sound. The often intense sonic experience of standing in the center of the square is considered one of the benefits of leading, and sometimes a guest will be invited as a courtesy to stand next to the leader during a song.
Source: Sacred Harp – Wikipedia