Unnecessary commas?

I was just writing this sentence:

You can't predict how people are going to react, or what's going to happen, so just make your move, and then observe, and appreciate what happens.

And I realised that the comma is unnecessary, one could write:

You can't predict how people are going to react, or what's going to happen, so just make your move, and then observe and appreciate what happens.

Is there any grammatical rule about whether a comma should be used here or not? Or is this more a stylistic thing?

Answer

Your comma is a serial comma, also nicknamed "oxford comma".
In this case it is more a stylistic issue if you use it or not. Sometimes it makes the sentences easier to parse (read).