Generally, link aggregation is used for two purposes: provide an increase in bandwidth and provide redundancy. Both aspects are addressed by aggregating several Ethernet links in a single LAG.
Under normal operation, all non-failing links in a specific LAG will become active and traffic is load balanced across all active links. In some circumstances, however, this is not wanted. Instead, it may be wanted that only some of the links are active and the other links be kept in stand-by condition.
LACP enhancements allow active lag-member selection based on particular constrains. The mechanism is based on the IEEE 802.3ax standard so interoperability is ensured.