Hi Snooze
The main difference between full backups with Backup Exec and CPS is that your full backup with Backup Exec is a point in time backup, and anything created between the backup and the failure is not backed up, whereas CPS allows you to restore to any point in time up to the failure.
As for if it's necessary to install CPS, that's really up to you and the business, depending on your requirements.
Hope this helps
Doug.