If you have begun or ended a line of machine stitching in the middle of your quilt, you have to deal with the two thread ends, assuming you don't want to leave them hanging (although if this is the effect you want, go for it; you might even want to knot a bead onto the threads to make it clear that this is deliberate, not accidental).
Some people backstitch to secure the threads, or perhaps use very tiny stitches as they get to the end of the line, then cut the thread ends off right there.
But I have seen too many such finishes that don't look finished at all. The scissors can't reach exactly to the surface of the quilt, so the thread ends stick up in little eyelashes. Or the backstitch didn't really secure the threads, so over time the quilting comes unsewed. I think it's much more professional to pull both ends to either the front or back of the quilt, tie them, thread them into a needle and make the threads disappear between the layers of the quilt.
This is time-consuming, of course, even if your eyes are good enough to thread a needle without difficulty (mine aren't). I have used self-threading needles but they tend to shred rayon or shiny polyester thread. It's much easier to just use a needle threader. As an alternative, quilter Robbi Joy Eklow champions an alternative method of sinking thread ends that really works.
Try both methods and see which one makes you happier.
My method -- with needle threader