Should you back up Google Drive contents?
George Crump of Storage Switzerland discusses whether it is necessary to back up Google Drive contents in this Expert Answer.
Do I need to back up Google Drive contents?
At first, this question seems very similar to an earlier question about backing up Dropbox, but the answer is actually slightly different. Google Drive, especially if you are using Google Docs, may need to be handled differently. If you are using Google Drive like Dropbox to sync non-Google documents, then refer back to the Dropbox backup article.
For user data, there are two basic reasons for backing it up: first, to recover from hard drive or SSD crashes, and second, to get to a prior version of a document you were working on. If you are using the Google Docs applications, you are covered in both of these instances. If your drive crashes, all you have to do is install Google Drive on another system and let the files re-sync. Deleted items can be recovered from the trash can. Just be sure never to empty it. Previous versions, though they have an interface I'm not personally wild about, can be accessed via the version history interface within the Google app itself.
So why do you need to back up your Google Drive? To protect your data from a problem at Google HQ, like a system failure or a service attack. All your data is on Google's storage. If they have a failure, like they did with Gmail a few years ago, you could be without your data for a few days or even permanently. In theory, it should be available on your local synced copy, but if you are unlucky enough to suffer a local disk failure at the same time there is an outage at Google, you could lose data. Another reason to make backup copies is to have a workaround to Google Docs relatively weak revision history and restoration capability.
So, do you need to back up Google Drive? I would say that if you are using Google Apps for most of that data, then no, you do not, unless you're just paranoid like me. If you are using Google Drive as more of a Dropbox type of product then, yes, you should perform backups.