when the string breaks after a fierce smashing session...

hehe besides the above occurence, usually depends on whether you
play regularly or not lor..
if regular, see if you very fierce player or what... if very
fierce, some may choose to restring every few months.... else,
restring once a year or when you feel that the racquet has lost its
tension... really up to individual player...
so how often do u play & where? 