uSync Action File
The uSync action file
Is placed in the root of the uSync folder whenever a delete (or certain type of rename) is detected by uSync.
The action file is used on imports to make sure we delete things that are no longer needed on the Umbraco site.
When you perform a full export, everything is cleaned from the disk, and recreated as an export. Prior to v3.2.3, exports would wipe the uSyncActions.config file as part of this process, but we found this could cause problems as the target systems then wouldn't know about any deletes that might have happened previously.
In v3.2.3 we have introduced an option to keep or delete the action file on a full export.
It is now recommended that you keep the action file on a full export, as this will make sure that all downstream installs of Umbraco will at least know of any deletes.
You will only want to delete the action file once you are sure that all possible orphaned items have been removed from all of your Umbraco instances.