For the most part, Retrograde and Reverse affect only TimeOffset Sounds. They are a "legacy" from early versions of Kyma, versions prior to the introduction of the Timeline (when one could implement Timeline-like behavior by introducing TimeOffset and SetDuration modules). These days, you can safely ignore those parameters for the most part (though they are preserved for compatibility with older files). At some point, they will probably disappear, so please don't create anything that relies on them.