Generally you use them to knit in the other direction. For instance, I've seen descriptions of square shawls where you invisibly cast on for the border in the lower left, knit a long skinny strip of border for the bottom, then put the invisibly-cast-on stitches on the needle with the other stitches and work back and forth across the entire width of the shawl.

The one exception is that if you work K1 P1 on the row after the invisible cast on, I think it won't unravel. I'm not sure it's a nice edge, though.