What's the difference between a managed team and an approval or review team?

The Manage Team action controls who has access to read and modify the object.

The Allow Access To setting is always set to 'Everyone'. You can select 'Team members only' and select users to have access to the object. So, when the Submit for Approval action is executed, some users, who don't have access to read or modify the requirements specification itself, may be notified of a Worklist task to Approve or Reject the object.