Balance is a gauge used by Avalon to determine your physical 'state of balance', or rather, how capable you are at any given time of executing a physical maneuver. Actions such as swinging a sword, firing a bow, stealing an item, will all leave you momentarily in an unbalanced state, recovering from the maneuver. While in an unbalanced state you will not be able to execute another action which requires you to be balanced. More complex actions take a longer balance time and the inately physical professions can learn to speed their balance when more highly skilled.
You may, if you feel you have fully mastered the concept of balance and understood its importance to your everyday Avalon life, wish to pursue ways of speeding it up: making yourself 'faster' in combat and complex action. Have a peruse of HELP BLOODLESS-BALANCE for example, to learn about an arcana directly relating to balance; or look through HELP GLOBESTAVES and specifically experiment with the effects of the FERTILITY power. These are but two of the myriad ways to impact your balance and that of those around you.