The inductor blocks the passing of high frequency AC current by storing the energy within the core.  For lower frequencies, it creates a large impedance over a broad frequency range and causes an impedance mismatch and actually reflects the noise energy back to the source.  For common mode noise, it uses the opposite direction magnetic fields to cancel out and thus remove the noise from the circuit.  Also, when a device is powered up or hot swapped, the inductor “chokes” the incoming current rush by slowing charging up the magnetic field flux which stops the passing of current until it is saturated.  Additionally, the choke allows the voltage to be applied downstream to ensure sensitive devices to get powered up prior to full current application.