What are the implications of changing organization-wide defaults and how do you plan and execute such changes to ensure no disruption of sharing access across different user groups?

Changing organization-wide defaults (OWD) in Salesforce has significant implications for data security and sharing access, and must be handled carefully to avoid disruptions and potential data leaks. OWD settings determine the baseline level of access users have to each other's records, and modifying them can drastically change how users see data across the organization. Therefore, any changes to OWD settings require careful planning, impact analysis, and meticulous execution. The most immediate implication of changing OWDs is the potential alteration of data visibility. For example, if the OWD for the 'Opportunity' object is changed from 'Public Read/Write' to 'Private', users who previously could see and edit all opportunities may suddenly lose access to those records they do not own or are not given explicit access through sharing rules. This change will affect all users and all existing records and can severely impact user workflows if not properly planned. Another significant implication is that changing OWDs can have a cascading effect on sharing rules. If the OWD is set to Private, then sharing rules are the primary mechanism for granting access beyond the record owner. You must check the sharing rules to make sure they are set up correctly. In addition, any custom Apex sharing logic will need to be tested after the change. This also includes....