The 'Default to previous' feature currently fills in a value when opening a new record or when editing a old record if that field is blank. This is very annoying as the user may unknowingly have entered data without realizing it by simply opening a record in edit mode and then saving it. 'Default to previous' is useful when creating a new record that is similar to the previous created record, but shouldn't apply when opening old records.

If there are situations that this would be applicable maybe add a second button to enable for both old and new records in app builder.