That's a seriously misguided approach that prioritizes feel-good recycling over actual building integrity. Denim insulation lacks the proper fire ratings for interior wall cavities and could violate code in most areas. You're introducing a potential hazard and calling it a value add, which is negligent. Proper soundproofing requires specific materials and techniques, not just stuffing random leftovers into walls. This kind of shortcut thinking is why so many DIY projects end up with moisture issues or failed inspections down the line.