Effortless. Precise.
These two words often seem at odds in a vocal group. On one hand, you want the choir singing with the causal, free approach of a solo singer who can make micro-variations in rhythm, pitch, dynamics, pronunciation. On the other hand, you want the ensemble to be unified, with a consistent approach to all of these musical elements.
They aren’t mutually exclusive. But they do require much conscious effort to achieve an effortless approach without ever sacrificing precision.
It is when a vocal group can successfully merge effortlessness and precision that they achieve the results that makes people so love listening to groups sing.