You can configure load balancing across 802.3ad links to provide quality of service (QoS). To ensure that QoS is symmetrically applied to all the links, the router periodically rebalances the traffic on the LAG. When you attach a QoS profile to the LAG, the load balancing properties that are configured are applied to the LAG, and determines how traffic is distributed.
For example, if VLANs are configured, IP queues are provisioned over the VLANs. In this case, the default behavior is per-VLAN load balancing.
For more information, see Providing QoS for Ethernet Overview.