TIP:
Sometimes we need to format numbers in a block of text, to send an email for example. We want comma separators:
1,000 — not 1000.

I’d always thought this required a custom function, and there may be times when you do want to manage currency symbol or precision, etc. (For example, this.)

There is a built-in function, though, that is all you need if you just want to separate the digits with commas: NumToJText

EXAMPLE:
NumToJText ( 1234567 ; 1 ; 0 ) gives us 1,234,567. Nice!