About Splitting an Area
Use the Split Area tool to define a surface patch or an edge to split from a board segment. You can then select this area when performing other operations. When you split an area you do not remove any volume from the part and no side surfaces are created between the driving and offset surfaces.
You can split an area to perform these tasks:
Selecting deformation areas that can be controlled during unbend operations.
Removing surface patches using the Surface Rip tool.
Creating an edge that can be selected as a fixed geometry reference.