What is the function of the hand wheel/balance wheel on a sewing machine?

The hand wheel, often referred to as the balance wheel, on a sewing machine serves the essential function of manually advancing the needle up and down. This feature allows the user to have precise control over the needle's position, which is particularly useful for starting and stopping sewing, backstitching, or positioning the needle exactly at a desired location.

Using the hand wheel, a sewist can gently turn it to lower the needle into the fabric and then raise it, which is critical for ensuring accurate stitching and preventing fabric from being accidentally moved while sewing. This manual control adds a layer of finesse and accuracy that complements the machine's automated functions, especially in intricate sewing tasks or when working with multiple layers of fabric.