Instructions that request you to baste, want you to temporarily sew with long removable stitches. Basting is the action of sewing a temporary stitch. It is achieved by making large removable stitches by hand or machine. The more you need to hold something together, the smaller your basting stitches will be but they are always sewn with removal in mind.
Machine basting is also used to ease in and gather fabric.
Basting holds something in place to test the fit or the look of an alteration help control fabric for final stitching. It is also used to temporarily close a seam as in inserting a zipper.
The lining fabric is slippery, so I will baste it before I do the final stitching.
The hem allowance on my pants is a bit wider than the pant leg, so I will need to use machine basting stitches to ease in the fullness.