Say you're working off a doc as a template and want to save a completely new version of the doc. When you sync changes up or down from Google Docs after renaming, copying, moving, or downloading the document, you'll be able to select whether you want to save the document as a new revision or as a completely new document with a fresh revision history.
When syncing up, if the doc was previously synced with a Google document, and then renamed, copied, or moved to a new location on your local computer, you'll be given the option to sync the doc as another revision or as a completely new document. If you simply want to create a revision of the document stored in Google Docs, click the first link. If you want to create a completely new document with a fresh revision history, click Version 1 of a completely new document.
Alternatively, say another editor has made changes to the document on Google Docs, and a sync down is happening for the first time. You'll be given the option to update your document by syncing the latest changes from Google Docs into your doc, or to create a new document. If you'd simply like to sync the changes down to the same doc, click Update your document. If you'd like to create a completely new document with a fresh revision history, click Create a new document.