These things hold your rotor to your hub. if it DID come undone, because it is a one-time use nut and didn't hold torque) what could happen??
Is it REALLLLLLLY worth the 8.00 or less to chance that? How many people would save 25.00 to use a used tire with half life left? not many... Same situation with this. If you want to use it again, know that these are responsible for pre-loading the bearings (will fail if insufficient torque isn't held), which in turn will ruin the hub if left alone, and in extremes can cause the entire assembly to seperate.
BTW: torque your *new* nut to 208-214 FOOT pounds.