I am sure that you have songs or pieces of music you either sing or listen to that are special to you. Sometimes, it isn't the song but the process that works for us like singing in the shower at top volume. It just feels good.
1. Listening to music while creating art helps keep the left brain at bay so over-thinking doesn't happen. Singing when you are on your own will make the creative juices flow. Really.
2. Studies have found that people who are ill are often helped by listening to music. This article talks about how singing to children in hospital helps them. Look at that wee face!
3. Even people working in technology are found to be more creative with music playing. Now I wonder if the same would hold true if they sang?
4. When we sing, endorphins or the "feel good hormones" are released. However, I have choir members who tell me that just looking out to an audience and seeing their enjoyment makes them feel good.
Singing is one of those activities that works with or without an audience. So why do you sing? If not, why not? Saying you can't is a cop out. Everyone can sing even my completely tone deaf Uncle Ed. It never stopped him from enjoying a good belt out of a song.
"Music washes away from the soul the dust of everyday life." - Berthold Auerbach