No tube should ever be considered useless. A use can be found for all of them, Sometimes it's as is, but most often (for me) it's in an unintended way. I usually have to think out of the box to make a tube work right.

Here's a tube that most would consider useless:

It sure looks useless, and as a stand alone image, I'm sure it is. What I did was change the step from 200 to 15, now I'm able to run it in a line to create a fuzzy edge for something. All you need to do is erase everything in the image that is not your fuzzy edge.

Here's the rug I made with a fuzzy edge from the useless tube: