The Principle of Relaxed Balance is at the core of all Martial Arts Training.
Maintaining a state of relaxed balance, while disrupting your opponents balance is the key to being successful against an uncooperative opponent (as in real life self-defense).
Relaxed Balance even while moving or shifting your weight from one foot to the next or when you are on one leg kicking, the idea is to maintain relaxed balance (Zhong Ding) at all times, whether you are moving forward or backward, left or right; up and down should always be maintained in balance.
In Taiji Quan and Bagua Zhang training I refer to this state of Relaxed Balance when you have developed a Neutral Posture which is readily able to transform force (energy) that it is in contact with.
Notes from a musical perspective:
The principle of balance in music is 'time'.
Having steady time is important no matter what the musical genre is and no matter what instrument you are playing.
It's not a guarantee:
Good balance while practicing = Good martial arts!
Good time in music = Good feel!
In music having steady time (meter) means you are able to play the piece (song) without speeding up or slowing down.
To assist in developing good time, most musicians will use some sort of metronome or drum machine for practice.