It really depends on the project. I do strive for accuracy and try to get better and better, but I don't usually rip out mistakes unless they're glaring and/or it's an important project and/or it's just an easy fix. I quilt for fun, all of my quilts are given away (except a few I keep) so I don't drive myself crazy over it.
Just this morning I realized a quilt top I had nearly finished had one block that was 180* off. I finished the top and tried to just leave it, but in the end I couldn't leave it there and had to go back and rip it out and put it back in right. This is a quilt that I made just for the heck of it and I'll probably keep it in the car, but I still couldn't leave that block backwards when I'd caught it so early in the process. If I'd caught it after quilting, no way I'd go fix it!