Should we stay tension-free during the delivery or not?

I’m more of a hitter than a pitcher and for me, it works always better if my swing is tension-free rather than trying to ‘muscle’ the ball. I also have black belt on Tae Kwon Do, and the kick or punch always works better with accuracy when it’s tension-free.

I’m not sure if it’s same or different on pitching. I had some ‘headaches’ or dilemma on whether to stay tension-free or not during my pitching delivery. What would be the better choice in order for better velocity? BTW, I’m not counting out scap loading