What happens when BTC is worth $10 million ? 
Then you won't get any change when spending $100 on a cheeseburger, since cents will be a forgotten memory at that point, and nobody will care that Bitcoin can't represent such trifling values.That's not necessarily true. When the economy grows, then the value of a fixed/deflationary money supply will grow with it.
For example, 1 BTC is worth about $1 million if Bitcoin replaces all the money in the world, and 1 satoshi is worth about $0.01. But then if the economy grows at about 2% per year for 100 years, then 1 BTC will worth about $10 million in today's dollars, and 1 satoshi is worth $0.10. The price of a Big Mac Extra Value Meal will drop from 399 satoshis to 40 satoshis.
This!
(have mentioned this before - can't find the post)
Here it is: Is it time to think about decimal precision ?Thank you!
[I'd say the Bitcoin transaction fees are much more worrying: As long as the minimum on-chain fee is 1 sat/byte, and users often pay much more than that, I don't worry about fractions of a satoshi. I expect high fees to become a problem long before 1 satoshi becomes too large to be the smallest unit.
What would happen to fees if the minimum amount on-chain was 1 milli-satoshi/byte ?
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My use cases for higher decimal precision are required today
My team are working to get IoT devices performing instant Lighting payments in an M2M network of fire sensors, alarm sensors, humidity etc etc.. These devices pay each other as and when they want a reading from any of the other senses. Thousands of sensors thousands of times a day, thousands of locations.
We already need lower than satoshi precision, and the idea of rounding up.. lol.. this is Bitcoin.