The only reason you pull up the bobbin thread at the beginning is to avoid getting a birds nest on the back. Many people leave the bobbin tails when ending a line of quilting and bury from the back. You can also pull up your bobbin thread at the end the same way you do it in the beginning but it can be difficult if you are one to make several teeny tiny stitches when finishing a line of quilting. You don't need to do that if you plan on knotting and burying so may as well skip the locking stitches and simply pull your bobbin thread to the top by leaving a generous tail and lightly tugging your top thread to coax the bobbin thread to the top.