If you use Google Drive's documents sporadically, the current system that syncs most of your files is probably fine, and you can still work that way. However, corporate users of Google's paid "apps for work" service may generate hundreds or thousands of files that eat up space on their machines. In that case, it makes sense to only keep working files offline and stow older files safely on Drive. It's also a way for Google to keep up with Microsoft, which has always had local file storage and vastly improved file sharing and online access for Office 2016. Google's new app features start rolling out today.