What are you trying to achieve in the first place?

Your email is safe when you do have a local copy and a full backup.

You didn't answer my original question! What don't you understand?

If the account connects using POP then you have a local copy.

If the account connects using IMAP then you must make your own local copy. The Local Folders account is useful for this.

In either case you also need a backup to make sure you are safe against accidents or hardware failure.