In which case the transformers should not be used? and In which case we are not advised to use Transformers?

The output of one transformer cannot be used as the input of another transformer in the same MAP step.

Transformers in a MAP step are independent of each other and do not execute in a specific order. When inserting transformers, assume that webMethods Integration Server concurrently executes the transformers at run time.

When exception occurs in a transformer, it swipes off the pipeline values and 'lastError' will not have the service stack too. So Transformer is not advised when there is a possibility of exception from the service used as transformer. Ex: addInts service, this would throw exception when there is 'null' input. So if there is a possibility that one value may be null, do not use transformer for this value transformation. Also addInts is a common service that can be invoked by many services. When an exception is caused by addInts being used as transformer - you can guess how tough it would be to track down the service that failed with the exception.

The above answer is partial correct and this is also one of the pitfalls of get last error. It will catch the latest exception and overwrites the previous exception, so we can’t guarantee all the exceptions are caught and accounted in getLastError.