To use groups with optional My library sync with Zotero server
For to use groups to share with colleages we must sync My library with Zotero server . It's not comfortable, better it will be not mandatory, as in fact there can be intimate or secret things in My library.
1) ONE - PER - ONET synchronization, with no use Zotero server ;
2) the technology of Zotero data independent image, all collections or selectively; Some utilities / function should allow synchronization between Zotero on your computer and portable image on an external drive. This must be synchronization, rather than just copying.
Syncing that doesn't involve Zotero server isn't going to happen for metadata, though (absent a full local Zotero data server install, which some people have--the code is open--but which is a major undertaking).
Yes, this is about sync without Zotero main or local server. As in other application such interaction is called one-per-one (computer - to -computer). So one per one sync without Zotero server. The reason that this is necessary, - a security of personal (group) data of researcher.