How to Bind Off Cables
Using Decreases Prevents the Edge from Flaring Out
I normally just use the simple 'knit bind off' method to bind off my projects, but with cables this won't create a good finish.
The reason for this is that cables pull the sides of your knitting inwards and create a more narrow piece of knitting (compared to stockinette stitch or similar). So if you then bind off each and every stitch, the bound off edge will flare out due to cable crosses not pulling the sides inwards anymore.
Therefore, to prevent this overly-wide edge, you will need to decrease as you bind off across where the cable lies underneath. This video will demonstrate this process: