Sql backup with local system services

hello i am configuring Sql database backup in win2008 server. As per the tech notes, it says to start the netbackup services with domain logon account that have sysadmin rights in Sql and local admin rights. But i did not do this and my backups and restore is working fine with netbackup services in local system account. Could you please let me know what is the difference in both the procedures. With local sysyem account how the backups are happening and with which user account.