PrincipalObjectAccess (POA) table is an important table which holds all grants share on CRM objects. This is just for understanding purpose.

SELECT TOP 100 [PrincipalObjectAccessId] ,[PrincipalId] ,[PrincipalTypeCode] ,[ObjectId] ,[ObjectTypeCode] ,[AccessRightsMask] ,[InheritedAccessRightsMask]FROM [PrincipalObjectAccess] WITH (NOLOCK)

PrincipalObjectAccessId – The GUID of share record.
PrincipalId – The GUID of the User or Team receiving the Share.
PrincipalTypeCode – indicates whether it’s a User or Team. --user
ObjectId – The GUID of the specific object being shared.
ObjectTypeCode – The object type of the record being shared.
AccessRightsMask – This field stores the rights granted directly via the ‘Sharing’ dialog.
InheritedAccessRightsMask – The rights applied by the system through cascading or reassignment processes are stored in this field.

check microsoft query to control this table data..

CRM PrincipalObjectAccess(POA)