Sewing Stretch Fabrics
The Manual, as with most stitches, recommends starting a stretch stitch with a basting stitch, which is a solid practice for best results. I skip the basting stitch in the demo video in favor of demonstrating the zig-zag stitch.
Generally, if one has a serger, one uses a serger when sewing knits or stretch fabric. The design function of a serger works particularly well with stretch fabrics, allowing for maximum stretch and flexibility at stress points caused by movement, like armholes, or ankle bands. However, a serger is NOT a necessary machine, as most commercial machines, include The Machine (Baby Lock Destiny 2) come with a zig-zag and/or overlock stitch function, which essentially serves the same purpose.
When stitching knits, a straight stitch is prone to popping when under stress. But a zig-zag stitch will stretch with the stretch fabric, rather than popping under stress. So while the manual includes tips for sewing a straight stitch on knits, it is far easier to use one of the many zig-zag stitch functions instead.