You could use it, but it probably wouldn't be very convenient. That fluffy stuff is basically Marabou, which is one of the most popular fly tying materials, the difference between the soft hookless barbs found on your hackles, and the barbs found on semiplumes like Marabou, is the rachis, the shaft of the feather the barbs attach to. You could make use of it, but you'd exert a lot of extra effort compared to making a fly with a new semiplume.
If you're conscious about wasting materials, just remember that the feathers you're using are already a byproduct to begin with. They don't harvest birds for feathers, they harvest them for meat, the feathers just happen to be usable in some other markets as well, but would be garbage otherwise.
If that still doesn't satisfy your conscience, then start saving just the hookless barbs until you have enough to re-stuff a pair of mittens. You could turn a pair of cheap synthetic mitts into a nice light pair of down-ish mitts, then brag about how you made them out of all the scraps from the hundreds of flies you've tied.