Joe at lesterbanks.com explains what Perfect Split does:
Perfect Split is actually a really simple solution (Charles is a really clever guy) where it will simply “cut” out a polygon selection in your Cinema 4D scene and Pastes it back in as a new object while leaving the original mesh with a hole. Charles notes that this is useful for creating things like sliding doors, a robotic arm or face panels etc. What it actually is, however, is a time saver! Perfect Split is a Python Plug-in and will be available for free download on c4dtools.