"I don't need backup if my data is in the cloud"
You probably do...
Cloud providers are fond of quoting their reliability figures which are typically '4 nines' (99.99%) or better and they WILL back up the data to help them achieve this in the event of a failure by restoring the data to the same state it was in at the point of failure - so they back up frequently but do not need to keep 'old' backups as they only need to restore to 'now'.
Typically the data stored in the cloud is synchronised to your PC so you work on the data on your PC and any changes are replicated back to the cloud storage. This includes any deletions as well as corruption or changes to documents.
Independent cloud backup typically copies your cloud based data to another cloud provider (unconnected with the original one), and also keeps unlimited archive copies so it is possible to go back to any 'point in time' - deleted a file 3 months ago, go back and find it.. Need to go back to an old version of a document, it's there. In many cases emails are also archived so you can retrieve emails that have been deleted.
In the worst case data can be restored to your local PC so even if your original cloud provider is unavailable it is possible to retrieve your archived data.
Our cloud backup provider supports both Office 365 and Google Apps....