In the Business subscription, there are additional options that allow you to choose who can contribute to group conversations.
This lets you get important information across to your team without worrying about employees posting unrelated or uneccessary info and getting off track.
When you create a new group conversation, you will see the option to choose who can post:
Everyone can post means anyone added as a member of the conversation will be able to reply.
Only admins and managers can post means any users assigned to the admin or manager role can add messages.
Only specified users can post lets you choose certain users who can add messages. A field will appear where you can give users access.
Any of these options can be edited at a later time, so you have the option to add or remove restrictions as needed.