Row counters help you to keep track of the number of rows that you have knit. You don’t [B][I]have[/I][/B] to have one, but they are quite useful if you don’t want to have to remember how many rows you’ve knit. I love mine because I can set down my knitting and come back to it later, and know exactly where I left off in the pattern.
As to the cable needle, it’s all a matter of personal preference. If you were okay with using the stitch holder, then use it, but a cable needle would be useful when making larger cables.