This setting allows you to block users from syncing files from consumer (Microsoft Account-based) OneDrive. By default, users are allowed to synchronize personal OneDrive accounts.
If you enable this setting, users will be prevented from setting up a sync relationship for their personal OneDrive account. If they had previously been synchronizing a personal OneDrive account, they are shown an error when they start the sync client, but their files remain on the disk.
If you disable this setting, users are allowed to synchronize personal OneDrive accounts.