That’s a brilliant idea: when you knit lace (but not only there) thread from time to time a different coloured, best slick thread through the stitches as lifeline.
If you have to frog, this thread makes sure that the stitches won’t frog further and I think that it should be easier to pick up the stitches, too.
But also, if you loose a stitch, it can’t go further than the lifeline.
I’m amazed! :))
Links:
The Lifeline