When should I reset the SMC on a Mac?

I want to know when I should reset the SMC on a Mac. I have a very quirky G5 and was wondering if resetting the SMC would fix some of its problems.

SMC is short for System Management Controller.

The SMC manages hardware conditions related to temperatures and power consumption. Therefore a reset can only help in problems that are related to such.

Possible cases where an SMC Reset could be necessary include (according to Apple):

• fans running fast but should not
• keyboard backlight, battery indicator light, display backlight or magsafe LED behaves incorrectly
• power button does not respond
• closing/opening the lid does not work properly
• battery not charging properly
• system unusually slow