I remember when we a couple of pieces of music written only in unison. After a few practices, the choir decided they didn't want to sing them in unison and so we found one in a 3 part arrangement and Elaine, one of our awesome sopranos, wrote the other in 4 parts. They really were more fun to sing and we enjoyed them both as did our audiences.
It is not easy for a choir to sing well in unison. If you have many different voices, the listening that must happen in order to create a great unison sound is really intense. In fact, I feel that it is almost harder to sing well in unison than in a multi-part harmonies.
Our choir is just under 20 voices strong and so each voice is very important to the overall sound. Each person and each unique voice adds to the richness of the result. We sing in 2, 3 and 4 parts sometimes splitting into as many as 8 parts in various chords. Because we sing in such varied styles and harmonies, our sound changes constantly. I love it!
Picture a "Dagwood" type sandwich. If you are old enough to remember Dagwood of Blondie comic strip fame, you will know that these were sandwiches piled high with everything in the refrigerator and then some. If you aren't old enough then "google" the word "Dagwood" and Wikipedia will fill you in.
Eating one of those sandwiches can be a real treat or a real terror. I usually have to use a fork and knife. I can make a huge mess trying to bite into something like that. Stuff shoots out the sides and it is just not pretty. I lose more than I gain it seems.
I feel that sometimes the music chosen by a group to sing can be like trying to eat that humongous sandwich. It can be rich in harmony and really yummy sounding. The dynamics are like the Grey Poupon and attention to diction and phrasing akin to a specialty bread. The result can be a really unique treat. However, sometimes, with too little attention the musical detail the sound can turn out like the tuna sandwiches my landlady used to make for my college lunches, white bread with tuna straight from the can oozing oil. The result is a pulpy mess assigned to the bin.
You really have to know whether the harmony and richness of sound suits the music you are performing. If you have the numbers and or the talent, then that harmony brings great depth to your understanding of the music. Harmony can become that sodden mass if not well considered.
Sometimes, you only want ketchup on that sandwich. Other times, the works is just right. I truly believe that our music is much the same. We have an opportunity to interpret thoughts with words and music and it isn't always appropriate to lather on "the works". Whether it is harmony, or loudness or even speed, too much can be like a Death by Chocolate dessert, way richer than necessary.
Even if you have a large group, your use of various, suitable arrangements and expressive devices should always be to give the song meaning. A big, rich, loud sound can be very impressive but like a "Dagwood", can be excessive and unmanageable at times. Variety is the spice that keeps us listening, don't you think?