I made about 100 bracelets and 90 or so monkeys fists over one winter and the children in my family love them, especially when they found out I made them myself. As for their practical use, I have used them for a bootlace replacement and have had a (cheap) tarp line break on me once in high winds - the bracelet came in very handy for replacing said line. I think they're largely fashion, but in a situation where you suddenly need a length of strong cord, they're invaluable - especially to bushcrafters, outdoor workers and tradesmen (amngst many others). There are many applications when out foraging, or coming across motherloads of wild food or wood, willow or kit breakages etc etc... they also have many emergency applications too.
As the materials are relatively cheap to source for just one bracelet, I reckon they're a useful thing to have on ones person.