Sink Group,use of sync

In Sink Group there is a “sync”.
sync: Indicates how fast the stream is to be rendered.
0: As fast as possible
1: Synchronously

I want to know with whom Synchronously?
and if sync=0,What are the disadvantages?
and if sync=1,What are the benefits?

It is synchronization mechanism in gstreamer. For live-source such as IP camera or Bayer sensors, since the source gives frames in static framerate, you can set sync=0 to disable the mechanism. For local video file, suggest set sync=1 to get smooth video playback.