Owner-based versus criteria-based sharing rules
Key Takeaway
If a requirement describes records by who owns them, use an owner-based sharing rule. If the requirement describes records by their record type or a field value, use a criteria-based sharing rule.
Sharing rules give certain users more access to records than the org-wide defaults allow. The two main types are owner-based and criteria-based. An owner-based sharing rule shares records because of who owns them. A criteria-based sharing rule shares records because of what their fields contain. To pick the right type for a customer, check whether the requirement is defined by record ownership or by record data.
What sharing rules do
A sharing rule is an automatic exception to the org-wide sharing settings for users in public groups, roles, or territories. Sharing rules can only open access, never restrict it below the org-wide default. You can create one only when the object's org-wide default is "Public Read Only" or "Private".
Sharing rules apply to new and existing records and to active and inactive users. If several sharing rules give a user different access to the same record, the user gets the most permissive level.