1) Settlement time (wires only sporadically free in US, plus usually settle slower)
2) Irreversibility.
3) The tradfi ramps, if used, only have to be OK with crypto ramp, rather than the whole host of underlying transactions. It is conceivable some banks will tolerate crypto while not tolerating, say, directly handling a particular transaction.
4) Lowered friction for international transaction
5) One or both sides can be unbanked.
<transactionFeeDiscussion>
Citation needed. I'm looking at the transaction fees for lightning network and they are in the range of FedNow or RTP.
For Bitcoin it's not even close.
</transactionFeeDiscussion>