They still are good eating, especially the pole types. Suppose growing a variety of beans is fun, boring to just grow one thing over and over. Purple might be easier to find among the foliage in some situations. Beans with stripes/mottling lose the purple striping too when cooked, still good to grow.

IMO there is no overwhelming reason to grow purple beans vs. green podded, other than their novelty. They both cook up green, and green varieties have far more variation in flavor, texture, pod shape & size, yield, disease resistance, etc.

That being said, one of the highest yielding snap beans that I grow (the heirloom Czechoslovakian) happens to have purple pods - as does one of the lowest yielding (Trionfo Violetto). The determining factor for growing any bean should be whether the flavor & performance meet the grower's expectation, regardless of color. I've grown "wax beans" too that tasted no different than green beans.

The purple color makes it easier for some to find the pods.

Point taken. I just don't know whether easy to find pods are worthwhile, if it comes at the expense of culinary quality. Not saying that there may not be good purple-podded varieties out there, but there can't be many of them.

Unlike purple snap beans, red or purple yardlong beans retain most of their color when cooked. Chinese Red Noodle makes an appealing side dish, a dash of vinegar turns the cooked beans to a beautiful burgundy red.