Dear Srihari,
Backup of Planning Area is not required to roll the horizon. Only thing you have to make sure is Users have to be locked and no other job (to planning area) should run parallel.
Also it is important to include this job as a regular process (process chain / scheduled Job) at the start of the week, from midnight itself.
But as a general practice, it is advisable to have regular backups as a fail save mechanism.
Regards,
JB