I did not know MacColl very well, but his presentation was well planned and excellent, there was a very good reason for him sitting in the position he did, it was to do with posture, something that is very important for singing.
    preparing yourself for singing is important, taking deep breaths increases oxygen to the brain, and calms the nervous performer, yawning relaxes the vocal chords, a few vocal warm up exercises can be useful avoid drinks with ice, ice constricts the vocal chords.