Chorus registration is used whenever the musical texture calls
for it; whenever the various parts would best be heard as equals
in timbre (tone color) and volume. Four-part hymns and the preludes
and fugues of J. S. Bach are examples of the elements of musical
texture that call for chorus registration:
1. there are TWO MANUAL PARTS OR MORE
2. NO part is prominent or more melodic in nature
The pedal may or may not be present.