What has been discussed thus far is correct. The disks seal (partially) the DO's prison and hold the taint on Saidin. Evidence recap: -- LTT freaks out and wants to smash every seal he sees -- Creation of the seals was simultaneous with taint So the tie to saidin is rather obvious, but as Morguen suggested is a way to cleanse saidin worth sending a Gholam? The answer lies in Fel's note to Rand. Something like, "Cleanse away the ruble before you can build again." Fel knew how to not just patch, but fully repair the prison. Rand will have to break the faulty patch, and seal the prison along with female channies. That's why a Gholam was sent.