Paul ...

"I remember a few years ago reading a review of a live concert in the New Musical Express, which stuck in my mind as a folkie. I can't remember the name of the band, but the reviewer said "... the singer was so bad that he had to put his finger in his ear to stay in tune ..."."

In that case we have a music reviewer who's not a musician, or not much of one, if s/he can display such ignorance.

"I still maintain that if your voice is good enough to hold a tune, you can do it with or without the "finger in ear", so perhaps it's more about a feeling of insecurity."

It's about what works best for you. Some musicians stand up to play, some sit down. One is not 'better' or 'more professional', it's whatever you feel comfortable with. In onstage monitors, some musicians like a mix with their sound to the fore, some to the back, some want the mix the audience hears. One is not objectively 'better' or 'worse', it's purely the preference of the individual, what they're most comfortable with, what they find most helpful. A cupped ear is very similar: it changes 'the mix' so that one's own sound is more to the fore - or not if your hand isn't on your ear.

"I think it looks better and more professional though if you can avoid it in a live performance." That's your view. I think ear covered or not looks fine and that it's not a matter of 'being professional' in the sense you mean. Being professional is putting on a good performance. If someone cupping or covering their ear helps them do that, then covering the ear is the most professional thing to do.

Do you really think my Bee Gees link above looks 'unprofessional'? I don't think the audience thought so (I didn't ask them), and neither do I.

It's about the *music*, surely?