Folders and synchronization

Sync-Only groups are good for syncing non-traffic group objects like you suggested. This could include users if you decided to create a users partition for all your user accounts to live in. It could also include iRules and Datagroups created in the partition assigned to the sync-only group. iRules and datagroups can be used from the partition by any other partition by the way of using the proc command in a different iRule or in the case of datagroups just calling them by /Partition/rulename. Another use case is in the case of DNS-Express in GTM. Its best practice to create all your DNS-Eexpress zones in a sync-only group because that just syncs the DNS-Express configuration amongst you GTMs.