Communication is all about acknowledgement.
Acknowledgement that the other person is worthy of your attention.
This goes not only when communicating face-to-face, but also for written communication.
Let me prove it to you.
What is your first reaction when you see an email with lots of typos? The best you may come up with is: "A casually written mail!"
And the worst: Delete It!
If someone has taken the effort and time to convey something to you in written form, it becomes your responsibility to put in similar effort and time to understand what is written. That's when good communication happens.