I find that grammar usage should be proportional to the seriousness of the conversation.
- Talking with friends (including IM and SMS) Grammar needed, low. I can always ask for clarification.
- Posting on a forum, BBS or Facebook? Grammar needed, moderate. I’ll make sure to be as clear as poss bile, but I may forget where the apostrophe goes or miss a homonym on my editing pass.
- Blog posts, articles and other unpaid/unsolicited creative works? Grammar moderately high. I need to be as clear and bulletproof as possible, but I may still miss things.
- Paid work, work communications, especially with outside individuals? Grammar needed, very high. I represent a business and need to make sure to represent them well.
- Legal, scientific or other scholarly papers, grammar needed, Perfect. A misplaced apostrophe here could undermine your entire argument or significantly affect many people.
It’s rude and unnecessary to apply the standards of scientific papers to my friends when we are discussing the latest Marvel movie. On the other hand if you are getting paid for your writings you need to not mistake figuratively for literally, unless it is intentional for style (quotes from teenagers in fiction, for example).
