Before the land on our farm was tilled drained...I remember my grand-pa, dad and uncle doing the same getting unstuck while plowing in the fall or when stuck in a rut with a manure spreader...it was also before 4wd tractors.
I used that technique once myself, but the post was chained the other way around, so the tractor was climbing on and over it to gain back some traction.
Works good, but needs to go slow.