There have been earlier non NASA attempts but each one has had "issues" with the launch vehicle failing. Hopefully this one will deploy properly and demonstrate the validity of the concept.
Even if only a few small ones were made to collect and tow space junk into deorbitting it would be useful. Larger ones might be able to hook on to meteors and tow them back to Earth orbit for collecting. They could also make sample return missions more practical as the return package need only need to reach Mars (or whatever bodies) orbit then get picked up by a Sail to return it to Earth orbit.
problem or using a sail to return to Earth orbit from mars, it uses the "wind" coming from the sun. A sail cannot go directly into the wind, maybe if the shape is done and used like on a ship they could tack back and forth and move towards the Earth, but as the parachute style it would only move away from the sun. and other stars.
Have loved the concept tho, loved the Space ship Jolly Rodger from back in an '80 comic book.