Clean Finish Raw Edges Before Attaching Front-Opening Zipper
When sewing fully front separating zippers (usually to the front garment opening), it is always more efficient to clean finish each garment raw edge individually prior to attaching the zipper.
Unless otherwise specified by your project, the simplest way to clean finish fabric edges and prevent from fraying is by using an oevredge stitch like serging or zigzag (available on your home sewing machine). In the example pictured above, a placket enclosed separating zipper is stitched to the garment's front opening. After the seam edges have been machine basted together to aid in the zipper alignment process, each individual edge is serged to prevent it from weakening and fraying during the garment's life cycle.
The zipper then shows though its construction process as determined by the type of zipper application. You'll notice that if you clean finish each raw edge prior to aligning and stitching the zipper, you'll feel a lot more and stability in handling the seam edges as the threads won't unravel or stretch out of shape.
You'll find that with most separating zipper applications, the zipper tape is aligned in such a way that clean finishing the garment's raw edges after the zipper has been permanently attached is virtually impossible, unless the garment is faced or lined. The zipper tape portions are often stitched or topstitched close to the seam allowance edges which does not allow enough space to handle these edges individually for clean-finishing.
You should follow the same logic if sewing exposed separating zippers. In this case the garment edges are handle individually through the zipper application process. Each edge should be clean finished prior to aligning and stitching the zipper. In the example above, a serging stitch is used again. If the finished zipper has been topstitched, as is often the case with exposed separating zippers, the seam allowance edges will be difficult to reach and handle in the clean finishing process.