I agree with the point made earlier, that the important aspect of the musical expression is the relationship of the intervals. Expanding on that thought, one element to consider in composing is "Do the written cadencesn fit the group?",for example if you wanted the bass section of a choral pieces to sing an ascending V- I cadence with deep low notes in the key of G, that might be a little out there skillswise for several of the basses. But you could transpose the piece one or two steps higher to accomadate for the stretch of range, obviously still applying the same accidentals to the piece. The same concept could be applied to a high saprano note needing to be lowered. The key of the piece should differentiate up and down due to the skills of the performers and their common timbre.