All communities tend to have both "laws" and "guidelines" and then "etiquette".

Laws tend to be enforceable and immutable. "No stealing."
Guidelines tend to be good ideas most embrace. "Always use a photo in a post"
Etiquette is subjective and full of opinions "unsolicited Follow For Follow requests are impolite"

All have value to a community, but can cause great consternation among peoples of differing cultural backgrounds, value sets and "morals".

But I think it goes bottom up - a generally accepted "etiquette" like keep your comments contextual to a post, evolves to a solid Guideline accepted by all, and can eventually become "the law of the land" if it gets enough traction to become expected and demanded by the community at large.

I don't know if I'm adding value on this topic with these observations, but I am throwing them out there as my point of view on where "etiquette" is important and forms the basis for our happy steemit society, thus it's importance and your seeking answers to it in this post is a good conversation to be having!