Prev min was 1k sats. Main use case is for wallets like Misty Breez, Bull or Aqua to be able to pay tiny invoices. As tiny as 21 sats, a very common amount used for zaps, at least so we heard ;)

Liquid Network fees won't get even cheaper any time soon as they just dropped by 90%, see https://blog.blockstream.com/confidentiality-made-affordable-elip-200-unlocks-up-to-90-lower-fees-on-liquid/