I tried piecing a quilt with the serger. It made the seams too stiff for my liking. A serger puts a lot more thread into the seam. Also there was more distortion when pressing because the two seam allowances are bound together; they couldn't ease to the side. This made the seams thicker and lumpier too. Next time I would make the stitches as long as possible to put less thread in the seams. I have seen nice tops that were pieced on a serger, so I know it can be done.
The biggest advantage of using a serger is the speed at which you can sew; sergers can move fabric *fast*!