What exactly does it do?
I tried researching but couldn't quite understand the function of it.

 

prevents heat soak.

 

it helps a bit by slowing down heat transfer from intake runners (which are directly attached to the heads) into the intake manifold, thus resulting in a little cooler IATs at any given time... but doesn't in any way shape or form prevent heat soak.

its pretty much (ill call this "plastic") a gasket that sits between the intake runners and intake manifold, isolating the 2 from directly linking metal-to-metal which can help with heat transfer

 

But in the summer, the trapped heat under the hood (aka, oven) will still get the intake plenum just as hot... even if you do have the Thermoblock spacer.

However, the opposite is true too. If you had the Ultimate Cooling Mod, then the Thermoblock Spacer is a "must have" addition. Once you have eliminated the high underhood temps (oven), then the only other source of heating the plenum is the heat transfer coming from the engine. The thermoblock spacer prevents this source of heating the plenum.


Here is some additional reading -

The Ultimate Cooling Mod (click here)
Outlaw Engineering Thermoblock Spacer (click here)
Throttle body spacer? Pros? Cons? (click here)
Insulating your CAI? (click here)
TB Coolant Bypass Mod...anyone do this? (click here)
Please HELP !!...Car sluggish or Flies(click here)
109 octane unleaded = 5mpg increase...(click here)
Engine Heat-Soaking issue (click here)

 

You are also increasing the length of the intake runner which alters the power band, from my experience, for the better.