Elbows are not useful body-parts for the choral conductor. Or at least, they are not helpful if they assert their presence in the conducting process. Clearly, having a joint between shoulder and wrist is useful, not just for the choral conductor, but for any human being who wishes to do things like scratch their head or put on a cardigan.
But the moment the elbow starts to be perceptibly present - if it flaps or sticks out - it starts to spoil the choral sound. Conductors who have sticky-out elbows produce a sound that is shallow and unsupported, the upper parts shrill and the lower parts foggy.
Conversely, conductors whose arms operate as integrated units, a clean line from shoulder to fingertip, undistorted by the protrusion of intermediate joints, produce a clean, resonant sound, with all parts integrated into an undistorted sound.