When and how much do u brace and tension your body is dependent on the task at hand.
Different movement tasks, activities, sports and endeavors require you to embody the right amount of tension to be performed in a more optimal manner.
Tuning your tension refers to the ability to bring the optimal amount of tension into the movement task at hand.
Of course the optimal amount of tension is still a spectrum or range, but this a tension spectrum can be narrowed over time and tuned specifically to the given task and/or to meet the intent of the task.
Lifting heavy weights leans way more towards a high tension or high- threshold strategy. Tension is purposely high, and often as high as possible. Irradiation creates additional stability and can recruit more neural drive and muscle into the lift.
Juggling a soccer ball is an activity where much lower tension benefits you. Stiffness and rigidity create chaos and poor performance. Relaxation control, and coordination require the right amount of tension to juggle optimally.
Boxing is a nice mix of both strategies. It requires micro-bouts of high tension to produce power punches, but only moderate amounts of tension for most jabs and sub-max punches.