Throw application errors (variable/output port)

At times one whishes to throw an error on certain condition. A rather obvious way to do is in an expression by means of the ERROR() or the ABORT() function. You can do this at two locations.

1. Output port: Be aware that this only works if the outport is connected to another transformation. Unconnected output ports are not evaluated at all. Possibly, this is an efficiency measure by PowerCenter.
2. Variable port: This works also if it is no further used. Be aware that if you do not remove unused variable ports, you bloat your mapping (code). I am not aware of an efficient method of detection of unused variable ports. It would be nice if PowerCenter would only execute unused variable ports if they contained the ERROR() or the ABORT() function.