It allows stock numbers to be reused without having dupiclates. My dealership recently reached stock number 10,000 so we started over with 100. Now there are two "T100's" an so on and so forth. Well, we don't want to delete all dupicates because the owners may still have their cars. However, it'd be nice to delete the vehicles that haven't been serviced in 5 or more years to alleviate this issue a little bit.