Provisional Cast-Off sounds very grand, but it is simply about securing your stitches so that you can remove your knit from the needles for reasons such as:
~ Measuring your knitting accurately, or trying it on
~ Attaching an edging such as a fringe
~ Grafting two pieces together, eg at the shoulders of a jumper
~ or you may even want to gather the stitches together
Don’t be afraid to remove your knit from your needles, just ensure you secure each and every stitch.
Put simply, using a blunt needle and a long length of yarn in a different colour, you thread it through all the stitches, and you can then tie the ends together to secure, and easily remove the needles. If you use a yarn no thicker than the one being used for the knit, then you can remove it and place the stitches back on your needles easily.
It is great practice to check your knitting regularly for fit and size etc, and removing it from the needles really helps making this far more accurate, so don’t be afraid, and have a go.
Sometimes you may find that you even create a different design by draping the knit on a mannequin whilst off its needles, as you can see other design options, and ideas.