I have seen musicians pour out their emotions while singing. Sometimes it seems as if the song reminds them of an unmerited favour or of hurt and pain. At this moment,they no longer sing to impress the audience, they sing to just pour out what they feel, and oftentimes this realm of music goes beyond entertainment, it becomes a message. I may not be good at music, but I've sung a few times in my local church. I noticed something different each time I allowed emotions to take the best part of it. I care less about my voice, the people, what others feel, and how well I sing using phonetics , all I just want to do is praise. This moment is priceless, it's the best moment in music, where you are yourself and just want to tell your story through the song you sing.
When a music minister suddenly starts to cry, or lay on the floor as they sing. Oftentimes their emotions start to take charge and all they just want to do is praise God with sincerity of heart rather than the praises that proceed from men. All that matters at that moment is whom the praise is given to, not themselves or the men who become judges over the performance of others. We rarely see this nowadays, musicians no longer include emotions, rather, they seek for perfection. So they train up their voices, go for choral rehearsals, but never take the time to digest the depth of the song in order to have a connection with it. Emotions in music is an expression of one's connection with what they sing, the more connected the singer is with the song, the more ease he sings it and with some display of passion and love that transits through the voice, body , and song.
As much as a good display of emotion gives positive volume during singing, a sad emotion can also play a negative effect. One who's sad does not give their best while singing. Their mood says it all as they sing with a squeezed face and a body movement that doesn't stir people up to join the section. There are a few times I've sung with sad emotions that didn't go well. There was disorderliness that could be sensed from how poorly I sang and how careless I was , in a hurry to see I was done. The harmony that comes with music was lost and this boredom was translated to the listeners who soon became tired. So emotions play a vital role in music. However, it depends on what kind of emotions was included, whether a connection with the music, that of joy or sadness. These can be felt from our voice and how well the music is carried.
There are choristers who smile while they sing. I never understood how smiling helped the process until I noticed the role of emotions in music. Maybe they smile to free up bad energy or probably calm their nerves as they sing, either way it helps them maintain a positive energy and allows them to stay engrossed in the song.