Having worked in corporate America as an Firmware Engineer and as a Technical Support Technician, I have noticed grammar is very important for a person to be taken seriously in that particular environment. Also remember much of the communication today is handled electronically and these communications need to be understandable to the recipient.

Proper grammar is very important in business situations, like applying for a job. When you go shopping proper grammar isn't required. If people understand what you want, they will sell it to you.

I agree it's important. If you are talking in person, it is not as important. But so much communication is electronic now, which makes it very important to be able to write clearly