- Restrict Managers to Certain Employees

While you can add additional manager logins to a specific account and limit permissions in terms of approving requests and editing schedules, these permissions are account-wide:  there is no way to restrict additional managers to only see or edit data for a specific group of employees.  

If you allow a manager to approve Time Off, they can approve the requests from any employee in your account.  Similarly, if a manager can edit shifts, they can edit any shift in your account for any position.
 
If you have separate locations or departments you are scheduling - the only way to restrict a manager to just change the employees or schedule in their own location would be to have each location in a separate WhenToWork account, since you cannot see or change data from one account when logged into another account.  BUT if your locations share employees then this approach is NOT recommended since the same employee should not be scheduled in more than one account since it could lead to doublebooking them and confusion for employees needing to have multiple logins to see just a portion of their schedule at a time.  More
 
Managers can change their email notifications to have email notices sent whenever another manager approves time off, or changes a published shift, etc if you are concerned with monitoring your managers' actions in other location's schedule. 

You might also want to add department codes to employee names (ie. John Smith might be listed with last name ‘ASB Smith’ and first name ‘John’).  Then the employees will sort by department, and managers will be reminded that the employee they are seeing on the Pending Time Off, Pending Trades, etc. lists that the employee belongs to another department.