Difference between VNTrackObjectRequest and VNTrackRectangleRequest

There are two options to use for tracking with VNSequenceRequestHandler, VNTrackObjectRequest or VNTrackRectangleRequest. Is that just a convenience or is there a fundemental difference in processing/logic by VNSequenceRequestHandler? Seems like its maybe just a convenience, if you are seeding it from an object detection than you would use VNTrackObjectRequest but if you want to just seed if from a rectangle than VNTrackRectangleRequest. Just curious if there is anything else to it.