OOPS! A quality pattern is the beginnings of a quality result. Quality is rooted in engineering and that's what the pattern is. If your pattern is crappy, you'll either end up with a less than stellar result OR you'll waste time correcting the pattern. For example, if the pieces don't match, you'll have a heckuva time getting everything to line up. There's a reason Coach pays their pattern makers in excess of $100,000 a year.
Pattern quality directly impacts sewing quality. No matter how good a stitcher you are, if the pattern is crappy, you're going to have trouble.