This function, accessed through Maintenance / Database Maintenance, will check all of the records for having "bad links", which are essentially links to records or pick-list values that no longer exist. Bad links can be a result of deleting pick-list items already in use, improper editing of raw data tables, program errors, and computer crashes/lockups. While bad links normally cause no problems, it's a good idea to clean them up once in awhile just in case they affect some function in the future.
Note that when you use this function there will be one prompt asking you if you're sure you want to do it, and then it will be an instantaneous action (more or less). There is no way to cancel it once it starts, so it would be a good idea to do a backup beforehand just in case.