Why would you put a comma after every three digits?
Native speaker’s answer
Rebecca
We use commas after every three numbers to make it easier to read the number. If we wrote 11,870 like 11870, It might be difficult to read for some. Or if this number 124,785,492 was written as this 124785492. It's much easier to read a number with a comma between every three numbers instead of no commas.