@south_korea_ln made a great list (in a reply) and I thought it deserved its own post.
Here are a few of the main reasons:
- convenience, just need to scan a LN invoice to accelerate your transaction to the front of the mempool.
- you can use it if your wallet does not support RBF.
- you can use it for some multisigs where RBF is not available
Original post here.