A production queue is where you "queue" up mass amounts of mats in a crafting alt's mailbox. End result, mailbox full of mats waiting to be processed:
When you have collected a crapload of mats and are ready to go to bed, unload the mats and start an afk craft queue:
Wake up, brush your teeth. Put your pants on and BAM. Who doesnt like to wake up to a few bags full of inks ready for glyphing:
Critical sure does.