Of course, the vocal muscles need some tension, like a piano or guitar string, or there would be no sound created. Also, the muscles must be toned and of sufficient strength.
Floppy and let go means there is too little tension for the pitch, and the muscles lack strength. We are not able to sing the pitch accurately. We would then feel that we let go too much and are floppy with not enough muscular activity.
Some results would be:
Rigid and held is an unfortunate attempt to gain direct voluntary control of the voice, which leads to over-muscularity. If our muscles are over-tightened and we have been trying to create sound by pushing and pressing, then we feel too rigid and held.
Some results would be: