It is useful in many instances to facilitate Collaboration, to question assumption of fact, to clarify and elaborate, and to build consensus. Used in that way, ThreadMode can lead to the building of ReallyValuablePages, the Opening up of WalledGardens and of incomplete or unclear ideas to integration with the rest of the wiki.
It can be fruitless and frustrating if the threads show no sense of ComingTogether, no Coherence, no LeadingToConclusionsAndAgreements, no OnlySayThingsThatCanBeHeard, and no AgreementToDisagree. If a ThreadMode page or several related ThreadMode pages cannot be refactored into a SinglePageDissertation? or a SplitofSupportedContentions (perhaps even by splitting to two or more pages), then it should be considered for deletion (with suitable notice of course).