what is the effect of teaching choral music with piano accompaniment?

Simply put, it's music for a group of voices. I for one sung in school choirs with polyphony (meaning many parts, not just the melody in unison, singing the tune and words together) two times and know by experience what it is. I sand as soprano in middle school in 6th grade only and in high school sang alto. (I did this in my senior year to help the music department out.) If you hear some, say, acapella pop from a medium to large group of people in polyphony, that's a good example of choral music.