Parachutes have to pass a certain amount of air for stability reasons. Material which fails the test by being either too tightly or too loosely woven is rejected, and comes onto the market.
It is a good 'poor mans' alternative to expensive tent cloth at around 0.9oz/yd. It is possible to waterproof it sufficiently well for it to be useful, using cheap materials such as diluted polyurethane varnish. This will flake eventually, but another coat each season works well. It does of course increase the weight of the cloth. It might also be worth trying proprietary 'wash in' waterproofers such as Nikwax.
It is also useful for making mockups and prototypes, where factors such as wind stresses and seam pulls can be assessed in the field prior to cutting expensive materials.
The panels look really cool pinned to your bedroom ceiling too. ;-)