Backup for apps is a really important because whenever you lost your phone or change your phone. With the help of icloud account you can restore your data.
icloud stores every app's data safely.
Some chats are really important for us. So there is a need for backup. So Where your Viber’s backup on icloud is stored. Go to settings, click on your profile and then tap on clear storage. In the list below there is your Viber backup stored.
If there is nothing important in your account you can clear Viber backup to free up some space of your phone. And unfortunately if you have deleted something important you can restore your data with the help of icloud.