At some point, perhaps once or twice a year, you might want to empty the temporary random phone number file, and start the process all over again.
One reason to do this is if you find some new or different Area Code and Prefix combinations you want to use, or if you want to delete some of those that you're presently using. Another reason is because a percentage, albeit small, of previously out-of-service phone numbers from 6-months ago, might today now be in service.
However, as DNA is very good at making sure you don't add or verify the same number twice, emptying out the temporary file too often could lower productivity slightly.
For example, if you empty it out too often, for no good reason, it is more likely that each time you generate random numbers, you will be generating numbers that had already been generated (and presumably verified) in previous sessions. Remember, DNA checks first to see if a newly-generated phone number already exists in the temporary random file, but if you've just emptied the file, there is no way for the program to tell if it existed prior to your emptying it!
For this reason, it's probably better to just continue adding new random numbers to the database, and only purge it when you get a new Area Code, or discover new or different prefixes which would greatly alter your existing random phones file. DNA can store about 10 million random records in 1GB of Hard Disk space. Most ComQuest Fileservers have anywhere from 10 to 20 gigabytes of free disk space available, so there's probably more room on your system to store random numbers than you have possible combinations of Area Codes and Prefixes in your market (unless you happen to have more than 1,000 Area Code/Prefix combinations!)