LACP uses keepalives, to confirm that both sides of the link are still in agreement on how to bundle and loadbalance the data, whereas a multi uses a static configuration. Also, LACP can dynamically reconfigure a link on error.
There are situations where either bugs, hardware error or operator errors (misconfig) can cause up to 50% packet loss over a multi, which would be automatically repaired when using LACP.
Greets,
Nils.
--
Simple guidelines to happiness:
Work like you don't need the money,
Love like your heart has never been broken and
Dance like no one can see you.