I follow the advice that Watebear has given you to only shock when you have combined chlorine over 0.5 ppm. Many others, including me, have given the same advice. However, Ben, the proprietor here, has advised on his PoolSolutions website that you should shock weekly, after a heavy bather load, after a known "fecal incident", and, if I recall correctly, after a heavy rainstorm. I think that the basis for his shock weekly recommendation is that it's just easier and safer to do it that way. If you're diligent about testing and maintaining adequate free chlorine you can probably do without it, but...

Poolsolutions seems to be down now so I can't find that article.

Cheers,
k