Well? Interesting question.
Grammar is (are?) the rules you need to learn so you can break them in such a way that you are considered to have your own writing style.
Michelle Baker, at Corporate Writing Pro mentioned a few books worth perusing toward this goal. I cut my writing teeth on Strunk and White's in college but here are a few others.
- Strunk and White’s Elements of Style
- Geoffrey Pullum in “50 Years of Stupid Grammar Advice”
- Fowler’s Modern English Usage
- Joseph Williams’ Style: Toward Clarity and Grace
The degree to which you can twist, bend or break grammar, depends on your knowledge of it, your audience, and your skill as a scribe.
How many brilliant authors have lived and written, died in poverty, only to be discovered by a later generation as a genius, all because they were before their time? It's quite socially subjective.
So, I think you have to write for yourself, what is pleasing to you and consider your audience, and your goal(s). What are you shooting for in your writings? Art? Money? Notoriety? Posterity?
I agree it certainly depends on what you are writing. Some styles are not conducive to some genres. Non-fiction styles may not work for fiction, yet they can and do. I'm not sure if we can quantify it.
But once you have it, you have it. And though it's hard to describe, as a Supreme Court Justice once foolishly said, "once you see it, you know it." But it is true to some degree, though not in all topics, to be sure.
I think it has a lot to do with your education (academically and experientially), as well as putting Malcolm Gladwell's "10,000 hour rule" (Outliers) into practice, which raises you to the level of expert which could be ten years. So start writing, and don't quit. I also find that if I think a piece I wrote was easy, it's usually not as good as if I put a lot of labor into it. However, I have had words simply "fall out of my head onto the page" that were thought by others to be extraordinary. The pulp fiction writer, Robert E. Howard (Conan the Barbarian, et. al.) said he felt like there was someone standing over his shouldar telling him what to write.
There is certainly enough room in the world for all kinds of things that make sense and defy explanation and almost always, an exception to the rule. But don't let that fool you.
So I still think it is important to learn different types of grammar and where they fit in. Then screwing with them until you have what is uniquely yours and works for you.
Now, go out and create singular expressions.