Instructor: If we had a really large number such as the population of Africa, it would be really hard to tell, at a glance, just how big this number actually is. It would involve a bit of a mental effort.
Outside of programming, we usually use the comma separators to make it easier for other humans to read such large numbers. In our case, if we add commas on every third position, we can now instantly tell that it's approximately 1.2 billion.
TypeScript also doesn't force you to use this feature in a specific way. You can add an underscore after each number, and you can even add them after the decimal point. Compilation won't fail, but it might make the code less readable, so it's up to the developer to use this feature responsibly.
For a more real-life example, I'm now going to write an amount input class. I'll create a private static at the top to indicate the maximum amount it supports and amount field of type number to store the actual entered amount.
I'll also create a show tooltip method that creates a tooltip and then hides it after a few milliseconds. Finally, I'll add a format million method that takes the current amount and returns the formatted string in millions.
Even though we've added just a few underscores to the numbers in this class, because we're working with such large numbers, we've made the overall reading experience a bit more pleasant and the overall cognitive load of someone going through this much lower.