Linear stitches, or individual stitches that can be used for lines, are always useful. However, I would call the Methodist Knot Stitch a 'thread-eater' as it is made up of two Back stitches of various lengths. Now is that useful or not? Only if you want to lighten your thread stash!
This is how to work it:
Take a long Back Stitch,
and then a short Back Stitch.
Then continue with the next stitch in the same way.