Everything is depending on Your enviorenement. I have no idea how much disk space do You have, what are Your offsite requirements etc.
In my env I do have frequency and it is set to 4 hours.
Please check out this docs, select the one for Your OS:
Core Guides
- System Administrator's Guide for Windows, Volume 1 ( http://seer.entsupport.symantec.com/docs/290203.htm )
- System Administrator's Guide for Windows, Volume 2 ( http://seer.entsupport.symantec.com/docs/290204.htm )
- System Administrator's Guide for UNIX and Linux, Volume 1 ( http://seer.entsupport.symantec.com/docs/290201.htm )
- System Administrator's Guide for UNIX and Linux, Volume 2 ( http://seer.entsupport.symantec.com/docs/290202.htm )
Look at volume 1 and chapter called "Staging backups to initial storage, then final storage"