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.