[hnfong]

Comma is required in modern Chinese. Nobody will bother reading your text if you don't at least put some of them in the right places...

(I don't know Japanese so I can't speak to that)

[throwaway2037]

Nice post. Can you give a simple example sentence where it is required? (I believe you.) I studied Mandarin and Cantonese for a few years, but I never got the level where I thought commas were required.

[hnfong]

Just a random text I had handy:

起初我見到一碟芽菜同西芹，以為佢上錯菜，用刀叉掘咗幾下，終於見到埋咗響底嘅叉燒。

Nobody writes it like this:

起初我見到一碟芽菜同西芹以為佢上錯菜用刀叉掘咗幾下終於見到埋咗響底嘅叉燒。

Can people parse the latter (with some difficulty)? Sure. The commas are not required to the extent that you can butcher the sentence even more without losing its essential meaning, but why stop there? You can remove even more stuff from it and still retain most of the meaning:

初我見碟芽菜同西芹以為上錯用刀叉掘幾下終見埋底嘅叉燒

But that's not how people write.