Windows Backup & Restore: What to Keep from AppData?

There's no universal solution to this question. No one will ever give you a comprehensive answer because there are so many applications. Each application stores its preferences differently, and you have to know for each particular application what it stores in AppData to decide whether it's worth saving or not.

Let me give you a couple of examples:

• Firefox stores its profile and general settings in AppData\Roaming. I think it's worth saving, the browser will be configured the way it was, including bookmarks, and even open tabs will be restored.
  At the same time the data Firefox stores in AppData\Local are useless: there are different caches.
• Opera browser follows the same approach. You find its generic settings in AppData\Roaming and (mostly) throw-away data in AppData\Local.
  Yet if you used Opera Mail client, all the mails are saved in AppData\Local, thus you may want to keep your mail messages.
• Microsoft Outlook stores its personal files with mail in AppData\Local.
• foobar2000 audio player stores its settings and playlists in AppData\Roaming.

Usually data in AppData\Roaming are more important than in AppData\Local.