In Salesforce, we have two types of Chatter Licenses. Below are they and small description to help you in choosing Salesforce Chatter license appropriate for your requirement.

Chatter Free License: User with Chatter Free License can access people, profiles, groups and files. They can make posts, view comments, upload & view files, join groups. But they can’t interact with Salesforce data such as accounts, contacts or opportunities.

So if you have a requirement of allowing people to only join groups, view/participate in conversation, please allow Chatter Free License to those people.

Chatter External License: Chatter External License allows people outside the organization, such as customer, into private groups in the Chatter community. Users with Chatter External License can –

  • see the groups they belong to, and profiles of members of those groups.
  • share files common to groups they belong.
Customers with Chatter External License can only be invited to a private Chatter group.
They can see-
  • Groups and profiles of the members of groups they belong to.
  • Files shared to groups they belong to
They cannot-
  • Post to profiles.
  • See records or other Salesforce information, even in search results.
  • Be followed. Additionally, customer can’t follow people or files also.
So if you have a requirement of allowing people outside of your organization i.e. your customers to join specific groups, please allow Chatter External License to those people.