What is the difference between near field export to OpticStudie and farfield projection?

What is the difference between saving the nearfield result from Lumerical and loading it into OpticStudio, versus using the far field functions in Lumerical?

The Far Field Projections in Lumerical allows users to project near field results to anywhere in far field free space. For example, if you want to determine the focal length (in free space) of a metalens, you can simulate the near field region around the metalens in FDTD Solutions, and project the result into anywhere in far field. However, to propagate the near field results through a macroscale lens system, OpticStudio is still required.