difference between model terrain in 3ds max and unity3d

As i am new in unity3d and 3ds max, i confuse why some people create terrain using 3ds max, what is the difference when we create terrain in 3ds max and plug into unity3d compare dirrect create terrain in unity? is there any difference in term of performance, poly counts, import export process, data accuracy, Texturing, materials, AI pathfinding, collision, etc??

The simple answer is that they differ in pretty much every aspect.

In the basis; a unity terrain will be runtime-composed off a heightmap. but a 3ds max terrain will rather be an imported mesh.

a unity terrain is created with an evenly spaced grid, a max terrain can have a geometry of any composition.

can you tell me more about the differ aspect 3ds max and unity3d?