A crochet provisional cast-on, in waste yarn, is a classic way to make a cast-on edge that you can unzip later, freeing up live stitches. A provisional cast-on is often used to start a shawl that will later need an edging knitted onto it. Being able to access live stitches gives a seamless join that cannot be achieved by picking up stitches from a regular cast-on edge.
The first crochet cast-on I learned was simple to describe: just crochet a chain of stitches in waste yarn; then pick up your knit stitches, in real yarn, into that chain. But it is devilishly frustrating and fiddly to pick up stitches into a chain that wiggles and twists. It won’t sit still and let you get purchase on the stitches. And if you don’t pick up a knit stitch in the correct “bump” of the crochet stitch, the “unzipping” won’t work in the end, and you will end up cutting that chain out of your knitting.
I had given up on the crochet cast-on until someone showed me this much easier way.
So simple, stable and sane. Works every time.