I have the same question. I'm not yet familiar with 3DC, I'm trying to pick a 3d sculpt application. I understand the purpose of retopology. But if I'm in a hurry and trying to model a rock or a large boulder, a polygon reduction program/plugin would be enough + normal maps on top.
Is this a mandatory step in 3DC ? For example with Mudbox - I can just import a model, quickly paint/sculpt some details and export back. Or you could just export the maps/normal maps. No retopology necessary.
Maybe it's not mandatory in 3DC. I'm just asking because everywhere you read about 3DC, this retopology step is also discussed. While in Mudbox you don't hear about this.