Well, fortunately for your neighbors most older furniture contains flame retardant chemicals with a dubious safety record. Nonetheless your garage will likely make quite a show as it burns, and fast.
For legitimate reuse in the insulation world look to Bonded Logic UltraTouch™. You can ship them a pile of your neighbor's discarded blue jeans, and feel vindicated for offsetting your personal contribution to consumer culture, without turning your garage into a roman candle:
UltraTouch™ Denim Insulation patented manufacturing process... These
fibers contain inherent qualities that provide for extremely effective
sound absorption and maximum thermal performance.
UltraTouch is also a Class-A Building Product and meets the highest
ASTM testing standards for fire and smoke ratings, fungi resistance
and corrosiveness. UltraTouch™ Denim Insulation contains
80% post-consumer recycled natural fibers making it an ideal choice for
anyone looking to use a high quality sustainable building material. (Source https://www.bondedlogic.com/ultratouch-denim-insulation/ )80%
Plus the stuff does not itch like fiberglass, and if fibers get into your lungs, your body will know what to do.
Yet another state has decided to ban certain flame retardants in
selected consumer products. Massachusetts has decided to ban more than
10 brominated, chlorinated, or organophosphate-based compounds that
provide flame retardancy to children’s products, bedding, carpeting,
residential upholstered furniture, and window treatments. (Source https://www.exponent.com/knowledge/alerts/2021/01/massachusetts-latest-to-ban-certain-flame/)
Now if that couch was a mattress, and in California, it would have a place to go:
California requires a statewide mattress recycling program designed
and implemented by mattress manufacturers with CalRecycle oversight.
The Mattress Recycling Council (MRC) is the manufacturers’ stewardship
organization that implements the program. (https://www.calrecycle.ca.gov/mattresses )
But it's a couch, and thus the best place for it is deep in a landfill, until the furniture industry steps up and starts to disassemble their old product for use in creating new ones.