I'm about ready to finish my high poly human model, and I was wondering why I see so many people using reotopo tools for reducing poly's on meshes as opposed to decimating. Using a decimate modifier seems so much easier and in the Youtube videos I've watched decimation performs comparably when accepting normal maps. Am I missing something?
If you do not intend to pose, animate or add subdivision to your low poly, then decimate should be fine. The topology that decimate produces is generally unsuitable for any of these tasks. Some software has automatic retopology (e.g. 3dcoat, zbrush), however even this is imperfect and an ongoing area of research.