Poets do it all the time.

Screenwriters bend the rules from time to time.

Um. . .well I guess those are the only writers who actually don't take grammar too seriously. Most of the short stories and novels I have read hardly ever waver either to the right or to the left of what the grammar rules demand. I'm referring to the exposition/descriptions/action (not dialog). So supposing you're not that good at grammar (like me) can you get away with that?

I think it depends. If you were to give a publisher a manuscript full of grammatical mistakes, you can bet they're going to laugh in your face. Most of the time they have guidelines on the type of FONTS they want to see, let alone basic grammar rules.

But there are definitely exceptions, I remember reading a book that had CAPS LOCK on for when something  SHOCKING was happening. It might have been Terry Pratchett, but I'm not sure. Then again, he's Terry Pratchett, so he can get away with it. 

LMFAO I would pay to see that caps lock story. That would have made me laugh so hard.

Terry Pratchett is great isn't he.  I think the least funniest of his disc world novels was Small Gods...and even it was still funny, but it was more of a darker edged humor. I'm not sure if it's possible for Terry to not be funny! 

That being said I can't say that I can really think of any time, when writing professionally, that it is good to do bad grammar...unless you are trying to write an accent, in which even that will be grammatically correct because of what you are trying to convey in the story dialog.

I think it would be very hard to break grammar rules when it comes to novel writing. The editor would most likely throw the book in the nearest trash bin or shred it to pieces if it has bad grammar and if the novel did not follow the formatting guidelines.

I think it depends on what you're writing really. Sometimes it's necessary to break grammar rules to be able to provide some sort of artsy feel to what you're writing/reading. Also it depends on the story you're writing, maybe you're story has some sense of, I don't know, different take on language or maybe it's part of the charm of it. I think if it's creative writing you can bend grammar all the way you like but if it's some sort of formal writing the you mush adhere to the rules.

Don't forget some people are famous for breaking grammar rules....but it may be difficult in todays world unless you can build a relationship with an editor/publisher/agent who will push it through as an art and not just laziness. Or publish yourself.

e.e cummings.
Emily Dickenson.
Jane Austen.
Charles Dickens.
More here.