style - Creative writing use and abuse

I am wondering what is the limit, if any, of justifying one's writing style as being creative.

I have often seen the use of a single word or phrase as a 'sentence' for creating impact. Example: "It was a large knife. Sharp and shiny."

Some other examples are starting a sentence with a conjunction (e.g. and) and using one sentence paragraph.

Question: Is it justifiable to disregard grammar rules for a specific creative purpose such as creating impact in the minds of readers?

Note: The above is usually not a problem to a person who does not speak English as his/her first language. English is my fourth language and I can tell you that. However, it may appear incomplete or incorrect to someone whose first language is English.

Answer

Grammar "violations" are perfectly fine in fiction, as long as they create the effect you desire in the reader.

Incomplete sentences can (sometimes) pick up the pace, or make the reading choppy and staccato. When you want those effects, use incomplete sentences.

Starting a sentence with a conjunction can (sometimes) make sentences flow together in an almost hypnotic way. They can suggest that the narrator is speaking/writing/thinking informally. When you want those effects, start a sentence with a conjunction.

For me, it's the same with every rule, whether it's a rule of grammar or a so-called rule of writing. What effects does following this rule create in the reader? What effects do "violations" create? Which effects do I want to create?