When I first started writing, I spent maybe 80% of my time writing new stuff and 20% of my time editing. Now? I'd say those numbers are flipped—20% writing new stuff and 80% editing.
My books are also much better. There may be a correlation.
That said, I still do not love editing. It's hard to pick apart my stories and put them back together again. It's hard to admit I made so many mistakes the first time around. It's hard to keep reading the same freaking book until it sounds like the stupidest thing ever written. The sheer redundancy of the task wears on me.
The hardest edit for me? The "last one"—the one right after finishing Big Changes and right before sending it off to whoever is waiting for it. Honestly, I used to be lazy and skip this edit. I still want to skip this edit! I mean, I've read it. I've changed the big things. I did a good job. Why is there this niggling urge to read it again just to make sure? Can't I just send it and be done with it?
Word of Advice: READ IT AGAIN.
Just do it. Really. I know it's annoying. I know you probably won't find a lot, but you'll find enough that it'll make a difference.
Trust me. Every time I thought, "Eh, it's good enough. Maybe I can get away with sending it now," I was wrong. I would inevitably get an email like: This is great! It's almost there. Read it one more time to make sure it's as clean as possible. I saw typos and some clunky prose, and the new sections you added need smoothing out. Make sure those transitions are seamless.
Then I would moan and groan because I knew that, and I still didn't want to do it. But I had to. And I didn't. My laziness ended up costing me and whoever had to read it valuable time.
Conversely, when I force myself to read it again and fix all those little things, I more often get a shiny gold star pass. And then I'm done! I like being done with an edit.
I've learned the hard way that editing your book into the ground is vital. If you're getting that impulse to read your book one more time, do it. Even if it feels like torture. It makes a big difference, so much so that crit partners, agents, and editors can tell. You will not get away with laziness. Just do the work you know needs to be done.