Solution: This is entirely dependent upon the data being backed up and the preferences of the admin and the storage.  Fragments are configurable from the GUI in NetBackup via both the Checkpoint configuration and the Fragment Size parameter in the Storage Unit config dialogs.  While the fragment size is allowed to go as low as 20 Megabytes, this is not advisable, as the fragmenting process creates a lot of overhead and may slow or possibly cause undesirable behavior in the NetBackup Media Server.  Extremely large fragments may also cause issues with the ability to span an image across Storage Units as well as other unwanted side effects. 

Checkpoint fragments can be created as little as every 5 minutes.  While this may not appear to be a cause for concern, the fragments are created over the runtime of the job, not based upon the amount of data in a given time.