Rib, or ribbing, is mostly used for its drawing-in properties, for example on the cuffs of socks or jumpers.
One problem that a lot of people have with ribbing is that the leftmost knit stitch on each column looks loose and messy. This is caused by the transition from knit to purl; the way that the yarn moves means that you end up with more slack between these two stitches than you do normally. There are a few ways to overcome this: firstly, you can just make a point of pulling the yarn more tightly between these stitches; secondly, you can wrap the yarn the wrong way around the purl stitch so it doesn't have so far to travel (you'll need to work into the back of the stitch when you come back to it on the next row, or it'll be twisted); thirdly, you can correct the slackness on the next row by gently tugging on the stitch following the first purl one with the tip of your needle, to spread the slack out a bit.
Corrugated rib is an interesting colour technique from [Fairisle]? knitting that doesn't draw in as much as ordinary rib.