How Important is Editing?
The answer is editing is absolutely the most important part of the entire process.
I make a point of supporting Indie (independent) authors and often buy their books for my Kindle. More often than not, though, I find that I can't finish their books. You've probably had a similar experience. How many times have you picked up a book and enjoyed reading it until you reached some point where you lost the desire to continue--and you still don't really know why? The characters were believable and the story started well...
Obviously the author hasn't been able to hold your attention for a reason, and there are a lot of reasons why this occurs.
Maybe it's too long and involved.
Maybe it contains a lot of spelling mistakes.
Maybe it's a good story but poorly written, and grammar is all wrong.
The point of view jumps around and confuses readers. (Head-hopping).
An information dump turns me off more than any other fault.
All of these could be improved with editing.
You can run a spelling and grammar check yourself, and we all know we should always make our manuscripts as good as we possibly can, but a good editor will pick up weakly expressed sentences and suggest improvements; recommend changes in lengthy, boring sections, and pick up incorrect use of words, e.g. Do you 'lay' or 'lie' on the carpet?
It's a fact that we cannot see our mistakes. We all need a third party to check our work. Even the best-selling authors rely on their editors.
Can Family Members Help?
A Beta Reader is someone who will read through your manuscript and correct punctuation, grammar, typos and spelling mistakes. They are invaluable because when we read the same thing several times, our brains become blind to errors like that. Friends and family members are often those people. They might even offer suggestions, which is great, but they probably don't know much about POV, OP3 and passive voice.