foreachRDD returning N RDDs when?

Question

There has been some discussion on foreachRDD in Spark Streaming as per a good posting stackoverflow 36421619. None-the-less I feel the answers are not clear enough when reading the prose. So here goes ...

My questions are:

1. When will foreachRDD ... return more than 1 RDD? With a sliding window over N batches?
2. If we process simply per batch then there is one RDD it is stated, so?

The commonest use case appears to be for persisting to external storage I note. That seems to be the guide for most, output operations. I am somehow missing something.

Answer 1

Only with windowed operation, else 1 microbatch = 1 RDD.