ᴠɪᴅᴇᴏ;
That depends entirely on what kind of performance you're aiming for. If he's interested in the mathematical-like side of musical theory, then he's likely someone who's looking to hit perfect, clear pitch every time he opens his mouth to sing a note. A crystal clear voice isn't always what someone wants to hear, however. Imperfections give a voice character and can convey emotion in ways the words to the song you're singing can't.
Where would Steven Tyler be without the scratch in his voice? Or the rough edges in Johnny Cash's voice? Or Janis Joplin?