Even speaking as an editor/proofreader and as The Word Doctor, I have to say in all honesty that grammatical perfection is overrated. "Always" is, in my estimation, an impossible goal, and usually is inappropriate.
Let me explain.
If you follow me on social media, you know that I constantly urge followers to carefully spell check and proofread their business writing, regardless of the medium. Whether a social media post, blog post, article, or email, you will be judged (right or wrong, like it or not) on how you come across to prospects. You may appear careless or ignorant when neither is true.
And yet your authentic style of communicating may be casual, friendly, and all your own. Using ellipses (...) rather than dashes or commas may be your "thing" and there is nothing wrong with that. Using words and phrases in a way that is authentic to you but not necessarily perfect AP style is just fine. You will reach those people who are drawn to not only what you say, but how you say it. Bottom line: be authentic!
There are basic rules of conduct, however: using their/they're/there correctly, lay vs. lie, proper punctuation and sentence structure, etc. Ignoring these customs is what gets writers in trouble. There's a big difference between stylistic and simply incorrect. "Incorrect" leads to not only judgment, but mis-interpretation of your message.
When you're writing casually for friends and family, as long as your message is clear I can't see why it must be perfect...unless you're even more of a grammar nerd than I am! But as I've stated so often, in business writing, perfection balanced with authenticity is the way to go.
Wisdom...or a great proofreader...understands the balance!