Argon/Krypton

Are these gases used solely to slow convection? Im curious to know if they serve other purposes, but I can only think of convection to slow the air movement/transfer.

the density of the gases also enables excellent noise reduction.

Krypton gas is almost three times more dense than Argon. It is also much more expensive to get than Argon is. Krypton is considered a specialty gas where Argon is an everyday gas we breath. In most cases one blocks sound better and the other blocks heat better. If your up to study some stuff way over the head of me. Here's the PDF file on a study done by some glass scientist's.
http://www.ktu.lt/ultra/journal/%20pdf_51_2/51-2004-Vol.2_01-J.Butkus.pdf

I apologize for keeping my answer so simple and understandable.