 <p>A primary key in database design should be seen as a unique identifier of the info being represented. By removing an ID from a table you are essentially saying that this record shall be no more. If something was to take its place you are saying that the record was brought back to life. Now technically when you removed it in the first place you should have removed all foreign key references as well. One may be tempted at this point to say well since all traces are gone than there is no reason something shouldn't take it's place. Well, what about backups? Lets say you removed the record by accident, and it ended up replaced by something else, you would not be able to easily restore that record. This could also potentially cause problems with rollbacks. So not only is reusing ID's not necessary but fundamentally wrong in the theory of database design.</p>