Resource groups fail over from one node to another. When this occurs, the original secondary becomes the new primary. The failback settings specify the actions that will take place when the original primary comes back online. The options are to have the original primary become the primary again (failback) or to allow the current primary to remain. You specify the option you want using the Failback resource group property setting.
In certain instances, if the original node hosting the resource group is failing and rebooting repeatedly, setting failback might result in reduced availability for the resource group.