Managing your imports is a complicated process. Almost all portfolio accounting data comes from custodial import sources, as opposed to manual data entry. In most systems, you lose the provenance of your data once the import has completed. You can't look at a specific transaction or client record and determine which custodian or import file the data came from.
Even if you can figure out where your data came from, what options do you have for fixing problems? You need high-level tools that let you manage blocks of data at the custodian or file level. If you import a bad batch of files, you need some way to back out information globally without going line-by-line through your accounts or having to restore a database backup.