sync degugging:
Clear Server Data-removes all bibliographic metadata from the server. The next sync will essentially "push" all of the client's current data to the server & nothing will be on the server to "pull" down. This is a useful work-around for unimplemented sync reconcilliation (deleted collections, etc.)
Reset Server Lock-I _believe_ that the server is locked when one client starts to sync, as multiple clients can't sync simultaneously. Presumably, this would clear a stale lock state.
Reset Client-removes synchronization information from your copy of zotero (last synced version, deletion logs, etc.).

Storage debugging:
"Reset storage history" - Makes local sync database forget whether files have been synced or not.
"Purge deleted storage files" - removes files on the server that you deleted locally.
"Purge orphan storage files" - removes orphaned files (e.g. files that aren't referenced by your zotero database).