Afaik the lightning network currently supports the 15th decimal place...
Cute, but unless
BTC is worth $10 million what does that realistically achieve? Where are you going to spend $0.0000000002?
Does that have a practical use case besides being a proof of concept?
This is something that will keep fees down.
If a txn has to pass through many 'hops' to get to its destination, each node will compete to have the txn pass through the node. The cost for one hop is low, but as LN matures, it will be more common for txns to have many (20, 50, or 100+) hops, especially to merchants with low transaction volume, and the cost to make the txn can add up. This plus the possibility that bitcoin goes up by 10, 100 or 1000x.