The rolling (or roller) foot is essential for coping with thick, bulky seams. The specific construction of the foot can vary according to your model of sewing machine, but the premise is the same throughout – a set of wheels or a roller mounted into a regular sewing foot. You might think those little wheels can’t make much difference in getting over an area were fabric has piled up – such as the crotch seam in a pair of pants, but you’d be surprised. If you’re planning to sew corsets, or make your own jeans, you want one of these.
In a pinch, it can take the place of a walking foot when tackling velvet or other piled fabrics. It’s not ideal, but it’s better than nothing – and it’s admittedly a lot cheaper than a walking foot. A rolling foot will set you back between $10 and $30, depending on your machine (unless you own a Viking, in which case the name-brand part costs $50 – ouch. Look for knock-offs, I say).
If you’re not sure which model of foot to get, go to a sewing supply place with the make and model of your machine, and they’ll set you up. Just be sure to get a roller foot and not a rolled hem foot, which is another thing entirely.