How will groups improve productivity?
On emails, it takes effort to ensure that everybody is fully informed about progress being made, decisions being made and the thought process behind those. Groups ensure that information is available to everyone without barriers. E.g. consider this email discussion we are having right now. No one apart from the three of us will know about the reasons behind how groups are better than emails. But if this same discussion was on a group, marketing / sales / support and anyone else can follow this discussion and talk about it confidently with others if needed. A large part of productivity loss can be attributed to the breakdown of communication. Groups solve for that by ensuring the information is available without barriers.