Tremolo in the voice can be used for effect, but I don't enjoy a whole lot of it at once. It's irritating in much the same way as auto-tune, but different. This guy , for example, sings a bit flat for a complete stanza, then auto-tune raises the pitch of his voice, attenuates the stretch and voila. I can hear auto-tuned voices, know they've been auto-tuned, then I slip into a valley of despair thinking civilization as we know it is crumbling and we are all doomed. People singing flat make my ears hurt; people singing auto-tuned makes my brain hurt. That said, we don't all experience the same things when we listen to music, or even experience the same things in the same way, and that's ducky with me.