Also having RAID or a Cluster makes no difference to need for a backup. Most data lost is caused by user error, also RAID or a Cluster is no protection against malware.
A nasty malware may have a timed later activation so that your backups are infected. Thus you can't just keep rotating the backups or just using one USB HDD etc.
You need to keep archived backups off site.
You also don't know how long it might be before user error deletion or mess of data, or patch or new program shows a problem. You may need an earlier backup than you imagine.
Most individuals, small companies and many Corporates have no real "disaster recovery" plan. What if your single shop or office is burgled, burnt down, blown up, flooded. You can buy new stock, office furniture and PCs. What about your accounts, supplier data, customer data / CRM, payroll, etc? Also do not rely on 3rd party "Cloud" CRM, Payroll or accounts. What is their backup, security etc? What do you do if you lose your broadband? How do you migrate to a different supplier. Can you make your own backups in case of error of one of your users, not just the failure of provider?
Cloud services may be essential for a Commerce Web site. Or two co-located servers in two data centres is cheaper than electricity and Fast Broadband to a single office. Cloud services or outsourcing for your core business, your backend data etc is really stupid. Banks are particularly crazy to do this.