"Sync with master" is a feature in Premium.Chat that automatically updates the availability schedules of both sub-accounts and profile accounts to match the master account's settings. This functionality ensures consistency and cohesion across all associated accounts, eliminating the need for manual adjustments of each account's availability. It is particularly useful for organizations or individuals managing multiple accounts, as it ensures that all linked accounts are accessible for chats according to the unified schedule set by the master account, thereby streamlining scheduling and avoiding potential conflicts or confusion among clients.