NOTE: For a video tutorial on backup and restore, see here.
If you've ever run into the situation where the fix for a problem is to clear your settings, you face a not insignificant task of redoing all those settings. It can be frustrating, especially if original problem doesn't go away.
What if you had a known-good backup of your settings? Then you could clear out the current ones and just pop in your good set. Easy.
IMPORTANT: Don't use backups for a different viewer. They're not compatible with each other.
NOTE: Some settings will not be restored. This is intentional; such settings are considered “dangerous” in that they can lead to crashes if set differently from the supplied defaults.
Settings not restored include your graphics settings (in Preferences → Graphics).
ALSO NOTE: Chat logs and transcripts are not backed up. To manage those, see this page.
This will back up all global settings, and the settings for the account you logged in with. If you have multiple accounts, with different per-account settings, you should do the above for each account.
Note: All settings are backed up, regardless of which checkboxes are selected. You can restore selectively.
Settings backup will store all settings for the account you are logged in with, be they global settings (that is, those that affect all accounts on a given computer), or “per account” settings. If you run multiple accounts and wish to have a backup of its “per account” settings, you will need to log in with each one and do a backup.
It follows that you can backup settings from one account and restore to another, but this will only restore global settings, since the “per account” settings refer to a different account.
“Per account” Settings are backed up to a folder with that account's avatar name, inside the backup folder you specify.