Apps Script access to auto-counter, triggered and calculated fields
Fairly simple: Apps Script isn't as useful as it could be without being able to access every field in each table. If you use an auto-counter or triggered field for a record ID, you are currently unable to load that record in an apps script (e.g. using loadrecord(), etc).
Nathan Waterman commented
I believe you can access a triggered field but in general I've been told that these restrictions are down to the order of operations; app scripts run first.
Not really sure why we can't reference a record ID field though. Or reference one of these types of field after creation of the record.