What exactly do they do? I've read that they can increase compression. My local dealer says they install them with all the cams...why would they do that? If you have set up your heads for the compression you want these would be useless...right? Is there any other benefits? Does it move the powerband any? I'm getting ready to do my BB build with Andrews TW44's and need to know if I should use one...only want to tear into it once.