Other than the fact of MC/AC or RX Greg is right. We have had this discussion before. My thoughts then and now were, if the piece of conduit is less than 10' it could be used for protection from damage, once you start to go over the 10' mark, you might just as well run the conduit and be done with it.
If you were worried and dissimilar metals and if the metal conduit will become energized, then why don't you use PVC. It would protect the cable and not worry about the rest.
