These are the notes for GoZync 3. Docs for the latest version of GoZync--GoZync 4--can be found here. GoZync 4 is a free upgrade and is highly recommended (hint: it's faster).
The reset makes GoZync mobile think that none of the local files have ever synced before. The main reason to do this is that if you download a new version of a mobile file set to "round trip", you may need to start the sync all over again to get your records down from the host. Without a reset, GoZync would only send you records changed since your last sync, which may not be what you want.
The second half of a reset is to reset GoZyncHosted. This will remove all the field level merge information for each user and clear their outboxes. To reset, click the "reset" button in the lower left of the Zync Logs. In versions before 3.16 manually run the script "Reset Hosted ZyncDB".