Orthographically? Pretty important.
Financially? Maybe even more so.
It should likely come as no surprise that I am a stuffy proponent of the serial comma (often nicknamed the “Oxford comma”), where a comma is placed before the conjunction and final item in a written list, as when there are multiple ways to do something in language, I generally endorse the one that’s less prone to ambiguity.
Typically, it’s little more than a stylistic preference, but as one dairy company found out a couple months back, this sort or ambiguity can have costly ramifications:
An Oxford comma changed this court case completely
(CNN) If you have ever doubted the importance of the humble Oxford comma, let this supremely persnickety Maine labor dispute set you straight.
Punctuation. It matters, folks! (>^-‘)>