A perennial question on community knitting boards is how best to cast on along a very long edge, such as a scarf made edge-to-edge (as opposed to top-to-bottom) or a wide afghan made all in one piece. IMHO, the best way would be to provisionally cast-on the long edge, using COWYAK or the crochet method. Afterwards, when the garment is finished, take out the provisional cast-on and work a bind-off to finish that edge. This has two advantages.
1. The tension of the edge can be adjusted afterwards to suit the tension of the garment
2. The two edges will match perfectly, both tension-wise and appearance-wise, having both been bound off by the same method.
(In fact, is my humble opinion that this is also the best way to cast on for pretty much ALL garment knitting--such as a bottom-up sweater. In other words, cast on provisionally, work the body of the garment, and only afterwards add the bottom band. You can then freely experiment with different bands--hems, ribbings, etc. Also by this method, The top and bottom bands will thus match along their edges, and the tension of the whole bottom band can be adjusted once you have a better idea of how the garment fits, and how the bottom band should best be tensioned to best fit the knitting of the body of the garment. A further advantage to this method is that it also allows you to fine-tune the length of the finished garment, as well as of the cuffs for bottom-up work; or the tension and height of the neck band on a top-down garment.)