When I first started to edit I refused to delete sentences or paragraphs. I would change the odd word here and there but nothing else. Over time I changed. Think of a film you may have seen that could have been better if it was fifteen minutes shorter or a book you have read that you would have enjoyed more if it was fifty pages shorter. When I edit I think of these things now and I delete large chunks of writing if I believe they are slowing down the pace of the book or have no real relevance. it is not easy to do but It is better leaving the reader wanting more than wanting less.
I also have a group of editors who kindly edit my books. They are lovers of books and all have good brains. If one of them says, 'I don't like this paragraph' or 'I am not sure that this bit works' I keep this in mind and review it myself. I may change it but I may not. It another person makes the same comment about the same part of the book I will change it, even if I don't agree with them. Obviously what I thought worked hadn't as two people have both highlighted it as a problem.
I find the hardest part of editing checking spelling, punctuation and grammar. My spelling is poor, I make silly mistakes in punctuation and I was never taught rules of grammar. This is why I write with a dictionary, grammar guide and punctuation book beside me. When I am writing my imagination runs away with me and I tend to forget the basics of writing until I remind myself! Fortunately word processors have helped me a huge amount but I make lots of errors because my fingers are not as fast my brain. I am also lucky that I have editor who it great when it comes to checking spelling, punctuation and grammar, but she is not editing my blogs which is probably a mistake!
The best part of editing and drafting is that it leads me to edit my plans for future chapters and books. By reading again and again a piece of writing other ideas form that improve my plans and I incorporate them. When I rediscovered 'The Adventures of Eric and Ursula' I updated the plans for all four books while editing it.
So, editing is functional not fun but it is necessary and really important. When I was at school and the teacher told me to check my work I never did but now I do it without even being asked.