The command C3DTOBLOCK is used to create blocks of Civil 3D objects.
For that he "explodes" the selected objects, but keeps the original.

The block will be on top of the original object.

will be useful when you only want one or the other object and the command "explode" Civil 3D can screw up the design. For example:
alignment that is part of a corridor any. If you explode, the corridor will be rebuilt without alignment. This powder be traumatic for large drawings.