If working with the web-based modeller (=SketchUp Shop or Free) one has the advantage of working in a cloud environment that has the ability to view and edit 3D SketchUp models, whereas Google Dive and Dropbox, for instance, are more storage services ( Google has some advanced documents editors for spreadsheets and word docs, but not for 3D models)
That said, it is wise to store on different locations to prevent the risk of loosing data. (Typically, a backup on the same harddisc has no benefit when it crashes)
Although the services of Amazon where Trimble stores the data is considered reliable and secure, it is recommended to have a ‘hard copy’ of your data.
(In fact it even mentioned in the TOS that it is not a cloud storage service!)
You can download each file or have your project automatically synced with Trimble Connect Sync, a desktop App that syncs your cloud data.
That’s for backup and securing your data.
While working in Free or Shop, it is wise to save regularly (if you have autosave disabled), be sure it says ‘saved’ after making alterations and especially before closing the tab.
That way, each save is stored as a version in Trimble connect and upon opening on another machine, you get the right version.