I can't believe I waited so long to do this...well, actually, I admit I was a tad nervous about going "all cloud," but I finally decided to clean up my Documents folder and just make Google Drive my default "save folder." I'm still nervous enough to not want all my information in the cloud (banking statements, etc.), so I didn't want to just move My Documents folder into my Google Drive; a nice midway seemed to make Google Drive my default save folder so I never have to worry about forgetting to put some file in there when I'm working on another computer.
The explanation below comes from here.
3. Make Google Drive your default documents folderYou might want to make Google Drive as the default documents folder considering the features it offers.
For Mac users, Open Terminal (in Utilities) and type cd Google\ Drive/. Hit enter, and then type In –s~/documents /documents. Hit enter again and watch the magic happen.
For windows users, 1)right-click on your Documents folder, 2) click Properties, 3) click Include a folder, choose your Google Drive folder. Finally, 4) select your Google Drive folder and check the option for Set save location. And that’s it, next time you save a document in a program like Microsoft Word; Google Drive will be selected as the default save location.