Further discussion about this here, and why it is needed: viewtopic.php?f=9&t=79783&p=421776#p421776
To sum it up, objects that require displacement on only particular parts of the object is not currently supported well - requires UV maps and image masks right now, which is a lot of work when other texture projection types would suffice. The ability to use vertex maps as masks for displacement would be very beneficial, and is something that is currently supported in Redshift. Using subdivision surfaces and doing all of the displacement in c4d so that you can use a vertex map instead of relying on Octane's subdivisions and doing displacement in the material has considerable negatives (harder management and having to manage multiple things instead of doing it in one place, lack of interoperability between Octane nodes and materials and features with the c4d system, extreme scene degredation and performance penalities when using lots of subdivisions, as well having the SDS constantly recalculating when moving around the scene or playing animation keyframes, etc).
Read the thread for further info. But that's the general idea.