Public groups let you share records with a set of users defined by criteria such as role, profile, or individual users. You can use public groups as recipients for email alerts in workflow rules or process builder. Reference: https://trailhead.salesforce.com/en/content/learn/modules/administration_essentials_for_new_admins_in_lightning_experience/administration_essentials_for_new_admins_in_lightning_experience_security_sharing