Most barbershop singers think that they don't need to have any skill in sight singing. In a sense, they're right. They can survive without it. But they end up losing a lot of time, a lot of confidence, and learning less accurately than they might.
In the beginning, barbershop singing consisted of four vocalists, typically men, improvising harmonies by ear to popular songs. There was no printed music to use, so sight-singing was a non-issue. As it became more organized, and local chapters and choruses began to form, the use of arrangements and sheet music expanded. Today, almost every song that is sung by a barbershop quartet or chorus is provided on sheet music. The importance of being able to read that sheet music has grown correspondingly.
Typically a barbershop organization assumes that its members cannot read music, and provides them with audio tracks to listen to. For many members, perhaps most, this assessment is correct. They learn the music from listening to the track, and the only thing they use the sheet music for is to read the words. Those who do this are missing out on some great opportunities. There are a number of advantages to the barbershop singer in being able to sing the part by looking at the sheet music, that is, to sight-sing.
Perhaps the biggest advantage is the time that is saved when sight singing is added to the memorization process. It is well-known that most people remember what they see far more effectively than what they hear. A skilled learner can look at a phrase on the page, sing it through, and then sing it with the track in order to memorize it. Since he learned it visually, he remembers it much sooner and more thoroughly.
Another big advantage is the confidence with which a sight-singer can learn the part. He knows that he is singing the correct part. Often the track is ambiguous; the listener can't tell exactly which notes are to be sung. If he can identify the notes on the page, he knows exactly what should be sung. There is no uncertainty whether or not he learned the correct notes.
A third big advantage is the greater accuracy possible in learning a part when you can read the music. Many singers learn the part by listening repeatedly to the track, without benefit of the sheet music. In this situation, the chances of learning the music incorrectly are great. The error is never discovered until the singer is recording himself for his section leader. Then he finds out that he's been singing the wrong thing. And it's so ingrained that it's almost impossible to correct. This doesn't happen to those with sight singing skill. They know that they're learning what's on the paper the first time. And they can record themselves with the knowledge that they've learned it correctly. Unless they experience a performance error, they are going to get glowing reviews of their recording.
Many barber shoppers recognize these advantages, but can't imagine that they could ever have the skill to sight-sing. It's unfortunate that such an easy skill to learn can seem so daunting. But those that go ahead and make the effort to learn this technique will find that the rewards are greater than they've ever imagined.