The three needle bind off is one of those knitting techniques that sounds a lot more complicated than it actually is. It's a helpful skill to have in your knitting toolbox because it combines joining two pieces of fabric and binding off into a single process.
This bind off is primarily used for sweater shoulder seams where you need to join two pieces of knitting, or two rows of live stitches, together. It's really important that both piece have the same number of stitches.
Pattern: Slipstream Cardigan
Yarn: HiKoo Sueño Worsted
Needles: Clover DPNs