I think he means the spacer that goes between the upper and lower intake. I know many people that use them, they are supposed to stop heat from transferring up i think. I dont have any proof if they make a difference in power though.
Forgot to add that all of them use tall valvecovers, so they need them for clearance too.
HUGE waste of money. They should only be used if you are trying to clear tall valve covers. It only makes the runners longer, so if anything, it's detrimental to performance on most applications.
I use a 3/8" intake spacer for clearance. The intake definitely takes alot longer to heat up, and maybe stays a little cooler at operating temp. A few guys at the local dyno told me the difference in temp with and w/o a spacer probably doesn't make any difference. If a bag of ice on an intake is worth 2-4rwhp (on my car) I wouldn't think the spacer would make too much of a difference.