The third reason is going to be temperature. With PWM fans, you can set custom fan curves in programs like Fan Control, so that if your CPU or GPU hits a certain temperature, the fan's RPM gets ...

Choosing the right fans for your PC build is more important than you might think. With the ongoing quest for quieter, cooler, ...

Of course, the standard way of controlling CPU fans these days is with PWM, so he built a circuit which essentially converts the PWM signal from the motherboard into a phantom thermistor.