"When singing solo and unaccompanied it's an affectation of the poseur-type, and completely unnecessary."
IMO Utter rubbish; most singers I have met find difficulty in maintaining pitch while singing unaccompanied - they tend to rise.
Tension is probably the main cause of loss of pitch control.
I assume you consider that the street singers, the Bengali temple singers, the Rumanian virtuosos, the callers to prayer on the minarets.... all of whom used (and in some cases still use) the technique "poseurs"?
Jim Carroll