It is a cheap answer for a windrower that attached to the rear side of a sickle bar on a mower for windrowing grain like oats, rye, barley, wheat and flax for combining.
It had two big drawbacks: One, the grain would rope together as it rowed off of the straps of metal being pulled by the sickle bar. When you combined the grain, if you came to a spot where the grain was real heavy, using the live-power didn't help as the grain was all roped together and it would just keep pulling it into the combine until the combine was all plugged up.
Two, the windrow would end up in the track left by the rear tractor tire when you were mowing, which put your windrow down in the dirt and rocks instead of up on the grain stubble where it could dry and you wouldn't run rocks through the combine.
An old grain binder with the knotter taken out worked much better for this, as you could lay the cut grain on top of the grain stubble up out of the dirt and rocks and it didn't rope the grain together.
- Del Parkinson