I like a 6 inch for baking banana bread, the larger sizes are too big for a loaf (If I had metal bread pans they would be better - but I have a 6 inch cast iron pan and not metal bread pans). Once in a while I'll put it on the grill for onions. However it is mostly too small. Even where it will work, the 10 inch almost always works just as well.
For dutch ovens, the small one is good because it stacks on the large one. However this is only useful if you are cooking on a campfire where you want to cook different dishes at the same time for a large group. I've never heard of them used for anything else and wouldn't expect them to be.