Subject: Grammar
We start learning to structure sentences once we begin to speak. However every language has their own rules for how a sentence is structured. We learn the more structured rules when we go to school.
When we write the rules are strongly observed and expected. But when we speak things change. We abbreviate or speak in fragments rather than talking like we write and observe the rules of grammar.
Shortcuts are always easier than walking around with the rule book in our head. Some have the ability to keep all the rules straight and use them even when they speak.
In my opinion for the most part everyone reads for entertainment but you still have those who will critique what they read. However, this is why we all have editors to help us stay on track with the grammar rules. As the writer it is our job to write and clean up after. Knowing the rules does help with the writing and keeps us from making simple mistakes.
I am by no means saying the rules aren't needed, what I am saying is the rules don't make talent or skill in being able to tell a story. You can be the best grammar rule follower and not have the talent or skill to tell a story.
I leave you with this thought, a writer is the creator and the editor is the clean up crew! As the writer the better handle on the rules makes the editors job so much easier.