I’m going to blather a little bit about register.
The fact that I used the word “blather” is a cue that the register of this post is informal. If I wanted to be formal, I’d say “This post is about register in writing.”
See the difference? The latter is stuffier, less conversational, more like what you’d expect to see in an article or a textbook, perhaps.
When I blog, post, or tweet, I get pretty informal. (See? I did it again. “I get pretty informal.”) I use acronyms and abbreviations and IDGAF who gets upset by them. I also curse, obviously. However, I can write in a very formal tone if that’s what’s required of me.
If I were writing an article for an organization’s newsletter–perhaps that of Copyediting.com, of which I am a registered member--I would certainly not use text speak or Internet shorthand, nor would I curse or employ nonstandard English. I would ensure my grammar, spelling, syntax, and mechanics were impeccable before submitting the work.
Unless, of course, the article was about text speak or Internet shorthand.
The fact that I’m writing in fragments (like that last line, just above) is another sign of informality. Fiction gets away with many things that more rigorous writing cannot. Dialogue is nearly a free-for-all, and that’s what makes it fun. Narrative runs on a spectrum from very informal to very formal, depending on the tone and subject matter. As an editor, I enjoy working with fiction more than any other writing, simply because of the variety it affords.
Research papers are formal. That doesn’t mean they should be incomprehensible, though. Using big words doesn’t make you sound formal. It makes you sound pretentious and, if the words are big but also incorrect, foolish. Stop it. Formal grammar/usage/syntax simply means a more restrained style, from working within stricter guidelines and rules. One watermark of formal register is paying attention to such guidelines as “don’t end a sentence with a preposition.” Yes, it’s old and hoary, but it’s also an elegance of formal writing. (It also means you may have to work harder to say what you want to say clearly, without tying the sentence in knots to avoid ending it with “of” or “with” or “for” or whatever. Do the work. It’s good for you and your writing.)
Consider your audience and your topic. Blog post about slang? Informal might be a very good way to go, unless you’re approaching it from an academic perspective; then you probably want formal. (What’s the blog? If it’s Strong Language, informality is not an issue. If it’s Lingua Franca at Chronicle.com, then something a bit more refined is probably in order.)
Writing an article for a professional journal? Formal is the way to go.
Dashing off a social media post? What’s it for? (OMG a preposition at the end of a sentence! Get the smelling salts, Ethel!) Are you just chatting, or presenting an opinion? Who’s the audience? What’s the topic? Register’s affected by all of these.