Damages of using the 3pin power connector on mobo.

What are the damages of using the 3 pin power connector to power a cpu fan? Why is it imperitive that I should use the 4 pin connector to power the fans? I'm just asking cause I'm not sure whats so bad about it.

It all depends on the wattage of the fan that you are trying to run on your motherboard. You shouldn't have any problems with a fan that is drawing 3 watts or less on any fairly modern mobo but some fans can draw over 12 watts of power. This would burn the traces on the motherboard or fry some components on it. You can still monitor the rpm's of the fan with a 3 pin to molex connector with a rpm sensor line on it. You can also do the same thing by splicing the 2 power wires from the fan into a molex connector and using the remaining (sensor) wire to plug into a mobo header.