The Parsec Client runs in borderless windowed mode normally (default=0). You can set it to fullscreen mode if you'd like to use "Spaces" on Mac or other features that are only supported on fullscreen applications. Set this value to 1 to enter fullscreen mode.
The Parsec Client can run also run in a window. The default is to run the client fullscreen with 0, but you can turn on windowed mode with 1.