Some choir conductors like to group their singers in "pods" of soprano, alto, tenor and bass. They feel that by equally dispersing the parts throughout the choir, they can achieve a better quality blend. Other conductors feel that they can control the blend of the singers better when they are in their homogeneous sections. I have sung in both arrangements and have enjoyed both models. The pod arrangement worked very well for a small choir of 40-60 voices on stages with very good acoustics. The blending was easily achieved because we were all very close to each other and could "feel" together easily.
Besides, it is very fun to sing in an SATB pod and hear all the parts so close around you. But unless you are very well tuned in to how you blend with your fellow sectioneers as well as your podmates, your voice may actually stick out from the fabric of the choir as a whole and you may not realize it.
For the Mormon Tabernacle Choir, I have the feeling that the microphone issues are the real reason we cannot sit in "pods." The blend that the conductor hears from the podium a football stadium's distance away from the choir is very different from the blend that the microphones pick up very near to the seats of the loft. I can just imagine how problematic the "pods" arrangement could potentially be. Individual voice colors regularly pop out of the choir sound even within our big sections. That problem could easily be magnified a hundredfold if we were sitting in pods. The guys in the sound booth can make an educated guess which mic is picking up the stray sound within a section, but it would be too hard to isolate the problematic sound if all the parts were coming through all of the mics. For us, the homogeneous sections help us unify our section sound for reenforcement and we rely on the conductor to keep us balanced with the rest of the choir (which we cannot always hear as well). This really does help us "feel" it together, too. And when we achieve that unity, it is truly magical!