Provisional Cast-On

Dear community,
what is a provisional cast-on and what do you use it for?

A provisional cast-on is often used when you want to join the cast-on edge to something else later on. For example, with a top where you start at the shoulders, this allows you to work toward the front first and then toward the back later without having to sew the stitches together afterward. Or if you want to make a double cuff, you can use these stitches to join the cuff together. 

A provisional cast-on is useful when you want to knit socks toe-up—that is, starting from the toe—and knit the toe using short rows, similar to the boomerang heel.