A general problem of empty secondary link is faced in service provider cloud. The primary link is runnnig out of bandwidth and secondary link is running as empty. If the tarffic works on load share or load balance form, customers might face the application issues. This situation is only overcome by traffic engineering.
Cisco provides the RSVP to implement traffic engineering tunnels but an another method is also there which is CRLDP which is not supported by cisco.
So next time when crunch of bandwidth is faced, implement traffic engineering in cloud.