If I tap Settings > Accounts and backup > (Google Drive) Back up data > Google Account data, one of the options is Gmail. Should I back up Gmail? I thought my messages were already being stored on a server (not my device).
Whether it's a Factory Reset, or a new device, once you login to your Gmail account & Sync, all of your emails will be available, except for emails you deleted.
When I go to one.google.com/storage, it says Gmail is using 160 MB. If I were backing it up, I supposed the amount of storage used in Google Drive would double.
Possibly, but backing up something that is already on Google's servers (I'm not sure if / how Google compresses what is stored) would be redundant.
If you could backup Gmail to a hard drive, that would be different, but unless you have some absolutely critical data in Gmail (hard copy?) I don't see the point.
I suppose that it's theoretically possible that all of Google's servers could implode, but..
