Provisional cast-ons are useful wherever you intend to pick up stitches later to knit in the opposite direction. I use them a lot in my top-down sweater patterns for casting on underarm stitches when knitting the body. Then later I pick up the stitches from the cast-on to form the underarm sleeve stitches. This avoids a seam underarm – so the finish there is neat and comfortable.
My favourite provisional cast-on is ‘crochet provisional’. I commonly instruct this method in my patterns because it is easier to remove the waste yarn in this method than in other methods I have tried. No prior crochet experience is necessary to master this method, just follow the steps in my illustrated PDF tutorial.