With the position hierarchy security, a user at a higher position has access to the records owned by a lower position user or by the team that a user is a member of, and to the records that are directly shared to the user or the team that a user is a member of.
The hierarchy security model is an extension to the earlier security models that use business units, security roles, sharing, and teams. It can be used in conjunction with all other existing security models.
Reference:
https://docs.microsoft.com/en-us/dynamics365/customerengagement/on-premises/developer/security-dev/ hierarchical-security-control-access-entities