hmmm ,,, looking back at your actual question,,
you DO need thermal paste,, the reason ,, it is the conductor of the heat ,, away from the cpu and into the Heat Sink,,
to keep the heat sink cool,, a CPU fan is connected to it,, the fan draws cooler air into the Heat sink and blows the heated air away from the CPU,,
Is it important? YES!
Conductivity is your best friend when heat dissipation comes into question,,
If you want to keep you PC running smoothly,, PASTE it!
Pads are OK,,, but past is better,,
cheers,,