Many people use the Yahoo email website but it does its own backup which does not always work. It seems that the only way to backup the email to your computer would be to use IMAP.
I know that IMAP keeps everything in sync. What would happen if someone deleted email while on the website? Would the Thunderbird version also be deleted?
This is the flaw that I see in using it as a backup. Let's say that you actually copied the profile as a further backup and later replaced it. Would it then sync with the online version defeating its purpose?