Every Subversion repository hosted on VisualSVN Server can be selected for several verification jobs — live repository can be safely verified by several jobs concurrently without service interruptions.
If you select to verify all repositories, the new job will always verify all repositories hosted on the VisualSVN Server instance including the repositories that do not exist yet and will be created later. All the repositories you create later will be processed by this verification job.
If you select to verify these repositories, you will have to select particular repositories the verification job will process. The new verification job will process only the selected repositories.