Autodesk has published an article explaining two uses for round-tripping between 3DS Max or Maya and Unity. In the first instance, they discuss white-boxing (a level in the Unity Editor, then switching to Maya or 3ds Max to complete the level; in the second example they talk about recording gameplay in the Unity Editor then exporting animation to Maya for an animator to polish, before returning to Unity to add the animation to a Timeline track. Read the article in full on Autodesk’s Maya blog.
If somebody only need to develop a browser game or application, he or she can use Verge3D directly with 3ds Max, without any round-tripping.