Since digits should be divided into four-digit groups in Asian number system, commas for every three digits in English are not useful at all. But Japanese people do use commas for every three digits, not for every four digits. The units of big numbers affect the phonemes of the last syllable of the preceding four-digit group. See the phoneme modification rule of small numbers. Here is an example of big numbers.
Blue letters indicate changed phonemes.
These are Japanese translations of American English large numbers.