The three Salesforce functionalities that are ignored when processing field updates in workflow rules and approval processes are:
Field-Level Security: This means that the field update will occur regardless of the user's profile or permission set settings that determine whether they can see or edit the field1.
Validation Rules: This means that the field update will bypass any validation rules that might otherwise prevent the record from being saved1.
Decimal places and character limits: This means that the field update will round or truncate the value to fit the field's format, without throwing an error