When to use saveRecord() vs. updateRecord()

Notice the different behaviors for updateRecord(record ) and saveRecord(record) .

updateRecord(record)	saveRecord(record)
Inserts new or updates an existing record. If a record with specified primary key value already exists, then updates the record. If not, adds a new record.	Inserts new or updates existing record. The client passes the old (unchanged) field values, so that if the primary key values are changed by the user, system can still find and update the same record.
Does NOT depend on `record.isNew()` value to generate UPDATE or INSERT like `saveRecord` does.	Does depend on `record.isNew()` value to generate UPDATE or INSERT
You CANNOT update a primary key if the new primary key doesn’t exist. It will just add a new record.	You CAN update a primary key if the new primary key doesn’t exist.