Within your CRM 'Settings'/'CRM Options' page, it is possible to restrict the visibility of contacts in relation to whether or not a user is the designated 'Managed By' for a record, via the 'User Options' drop menu (Fig.1).
Fig.1
The following provides a description of what each option entails for your users when it is selected for your CRM. Please Note as mentioned in section '8. Record Security', where contact fields have been restricted, only the designated 'Managed By' for a record will be able to amend/update those fields no matter which 'User Options' have been chosen for your overall CRM settings;
Open
View/amend all records, whether they are the managed by user or not.
Restricted Own + house
View/amend only own managed by records, can load House (& House Equivalent) managed by contacts in ‘Search’, but can’t actually load/view the contact. Can change own managed by to House (& House Equivalent).
Open & House Restricted
View/amend any 'Managed By' contacts, can't change the managed by on other's accounts, can only change own to House (& House Equivalent), and cannot set House to other than own.
Own + House + Department + No Department
View/amend where the user Managed By is the user's own/house/other people in own department & where managed by user has no department. Still can't change Managed By where already someone else even though own department.