To answer that lets take the total worth of the globe. According to this source https://en.m.wikipedia.org/wiki/List_of_countries_by_total_wealth
Total worth is estimated in 418 trillions.
We know that can exist 21 millon of BTC.
Then 418T / 21M ≈ 19,9M USD/BTC
This is the total purchase power that can has 1 BTC at this value of dollar (2021).
In satoshis this is 19.9M / 100M ≈ 0.2 USD/SAT.
That means that if you have 5M SAT and Bitcoin become global currency then you should have a purchase power of current 1M USD.
But if that is not enought you remember. Bitcoin is ultimate hard money, that means everyone is less scarce that Bitcoin, food, Cars, houses, people need make this stuffs and with more good and services But equal Bitcoin means price of this things will go down.
In short, when you purchase sats you are adquiring a extremely scarce good that not only can growth 38000% also can growth 3 or 4% (according to global production) yearly ad Infinitum.