Let's address some questions you might be having.
"WHAT'S THE POINT OF EDITING?"
No writing is ever perfect and anything you write or create is going to need another pair of eyes to look at and make sure it's actually saying what you're trying to say.
"WHAT I'VE WRITTEN ALREADY SAYS WHAT I WANT IT TO SAY."
It might not, actually.
When you've worked on something for days on end, crafting the story you're trying to tell, it's easy to stop noticing little details and see what you expect to see. You've been staring at it for so long, you're used to what it's saying and forget that you used the word "abundance" one too many times in the same section, or that you say "specialize" here and then "specialise" two paragraphs down.
You're attached to what you've written and you'll read what you think you wrote.
"NO ONE WILL NOTICE OR MIND A COUPLE OF MISTAKES; IT'S GOOD ENOUGH AND I DON'T HAVE TIME."
You may be okay with a couple of minor mistakes since you know what you wrote, but readers are seeing this for the first time and little errors make a big impression.
If you've written something, it is meaningful to you and it bears a message or a service or a product that you want to relay to your audience. Having a typo will affect how they view that message. Do you really want to lose a potential customer or reader because you typed out "salt and fresh ground black people" instead of "black pepper", leading to Penguin Publishing destroying thousands of copies of this cookbook from their inventory? (insert link here)
Besides, unless they're required to read what you're writing, people won't have the patience to parse through a badly placed comma or bad flow.
"WHY COME TO YOU SPECIFICALLY? I'VE GOT A FRIEND/FAMILY MEMBER WHO'S GOOD WITH WORDS.
Trained & Specialized
I'm specifically taught and trained to spot errors, grammar issues, word flow and other writing concerns that will disrupt getting your message across.
Advocate for Writer and Reader
I see what you're trying to write, I see what you actually wrote and I make sure both are in sync.
I want the writer's message to be clear and I want the reader's experience to be pleasant as he receives the message.
It's My Life
This is what I do for a living. I'm dedicated and passionate about the work and I never stop learning more about the craft.