What are the advantages to block off plates? Might be kind of a stupid question but was wondering if there were good power gains from doing this?

 

There are no power gains directly related to Block Off Plates. The plates purpose are to cover openings when removing components from the engine bay.

For instance, when installing a midpipe, you can remove the airpump and the ACV. If you remove the ACV, there is a large opening left on the Lower Intake Manifold which needs to be covered. That's what a Block Off Plate does, covers the opening left behind when removing unused components.

 

There are zero advantages. People just use them if they removed something that they no longer wanted/needed and it left a hole in the intake/exhaust track.

 

just clean-up. . . thats all, but its worth it