Some stuff to think through would be if there was one failure in a batch of many and it all ran again is the result the same and does the SDK throw any exceptions?
For a process that's just modifying some content or adding attributes it's as simple as adding the annotation.
But when it modifies some external resource you sometimes have to take care to make sure it'd do the right thing if there's a failure.
I think the Fetch won't require any code changes. Not sure about Delete or Put.
SupportsBatching: This annotation indicates that it is okay for the framework to batch together multiple ProcessSession commits into a single commit. If this annotation is present, the user will be able to choose whether they prefer high throughput or lower latency in the Processor’s Scheduling tab. This annotation should be applied to most Processors, but it comes with a caveat: if the Processor calls ProcessSession.commit, there is no guarantee that the data has been safely stored in NiFi’s Content, FlowFile, and Provenance Repositories. As a result, it is not appropriate for those Processors that receive data from an external source, commit the session, and then delete the remote data or confirm a transaction with a remote resource.