This scope lets an app "View messages and other content in private channels that your slack app has been added to"
This OAuth permission scope works with these Web API methods and Events API events.
channel_history_changed - Bulk updates were made to a channel's historygroup_history_changed - Bulk updates were made to a private channel's historymessage - A message was sent to a channelmessage.groups - A message was posted to a private channel