When inserting the zipper in this dress (which I still haven't photographed on me... bad Jenny), I ended up with this, despite using my usual matching technique:
The match between top and botton was off by about 1/8".
I tried to convince myself it was good enough, but I wasn't happy with it. After a few hours of thinking about how much I didn't like it and how much time it would take to fix (hours, I was sure), I bit the bullet and ripped out a 3" section to adjust. I timed myself.
10 minutes, including ripping, is the time it took to fix this zipper.
So go for those little fixes that will make you happier with your projects! I'm pretty sure this applies to cleaning things in my house, too, but I'm not ready to make that leap yet.