Surely you know how often I urge you to proofread everything you write. Proofreading will turn up careless errors in spelling, punctuation and grammar, as well as typos. Yes, you should still check for all of these, but editing goes beyond that.
Editing makes certain your writing is clear. Are you sure you are conveying the message you intended? Have you assumed your readers know what you know? If so, then why are you writing? You are imparting new information. But you have to be confident you are not confusing your readers, that your information that is new to them is presented logically and cogently.
Editing makes certain your writing is concise. Look for digressions and extraneous words. Get rid of redundancies: last but not least, at this point in time, absolutely complete, true fact, four P.M. in the afternoon, new innovation, blue in color, exactly identical, etc.
I have noticed that when I edit and change wording or move things around, when I then reread what I’ve written I often find I have left a word out or need to remove a word I had inadvertently left in when I revised. This is the time to read your text out loud (quietly, but still audible to you) and one. word. at. a. time. That way you will send your document out without embarrassing glitches. If you read at your normal silent speed, you will very likely speed over them.
Remember, revise comes from the Latin, to see again.