There are some very good uses of Google Docs. It is a word processor, spreadsheet, or presentation program and can be an alternative to Microsoft Office. Some use it is a way to backup selected files online. It also is a way to share selected files among users where these users have the ability to make changes to the files or view only. You can backup files (up to 1GB free) here and share any files. Google Docs is a cloud application. All files are stored on Google's servers. You access them on the internet therefore in the cloud. You can set up folders on your Google Docs site and treat it as another drive but this one is in the clouds. For $59 you can purchase an app that makes Google Docs your "G:" drive on your computer. On Google's page regarding this I see nothing about being able to sync files on your hard drive with Google Docs and vice versa.
Let's start with the backup feature. You do have the ability to backup selected files on your Google Docs account. You can drag the files you select to the indicated box or clicking on the "Select Files to Upload" link. Note that at this time you have to upload individual files. You cannot upload by folder. You need to select all the individual files in that folder. Personally I find this to be a disadvantage and why I would not use this to backup files per se. Further if you are password protecting a file, Google Docs will not allow you to upload it to its site. Currently Google allows up to 1GB to be stored free of charge. However files saved in a Google Docs format are not subject to the 1GB limitation. There is no automatic backup. You need to upload the updated file(s) manually. Note that you can purchase additional storage. 20GB is $5 per year and 80GB is $20 per year. You also can purchase additional amounts.
Like Libreoffice, Microsoft Office, Google Docs also is an office software suite. Google's suite includes a word processor, spreadsheet editor and presentation program. Like most office software suites, it supports the basic Microsoft (MS) Office programs (Word, Excel, PowerPoint). A big advantage of the Google Docs software suite is it can be shared, edited and opened by multiple users at the same time. This is a good feature when you are working on a team project for work, school or otherwise that involves a file(s) that all need to access and edit. When my wife and I are preparing for a trip, we will put a "To See" list on Google Docs for that trip that both of us can add to and edit . This sharing capability is a factor in why usage of Google Docs has increased. There are templates available for your use as well.
I personally like the sharing option the best. I talked a little about this in the previous paragraph. There are 3 sharing options. One is only where you and only people with permission can sign in to access the file. The second is where anyone with a link to the file can access it without signing in. The third sharing option is where the file is public on the web. Anyone on the internet can find and access it. You also have the ability to decide whether or not those with access to the file can also make changes. This is for any of the 3 sharing options. With a smartphone, files can be edited on your phone by you and others you allow to edit. For those who do presentations, this is a great way to email attendees notes from your presentation. You give those views view access and email the link.
Google Docs is a good application of Google especially when sharing files between users. Try it for your next team project.