I'm often guilty of grammatical errors: mostly leaving out entire words because I don't type fast enough to record what's running through my head. Occasionally, I slip on past/present tense when I rephrase too many sentences at the same time; it's something native Chinese speakers have issue with because there are no past/present/future participles in Chinese.
Either way, why do I care?
Ever receive a work email with spelling mistakes? Did you feel yourself lose respect for that person? Perhaps you won't admit it. But I bet there's a higher chance people remember the spelling mistakes than the email content. Imagine what a client would think.
Aside from writing well and clear, attention to editing should be given to blog posts, emails. It shows the reader that you care about the quality of their experience, that you take pride in your work. Because if you don't, why do it at all?