The purpose for the C-130 is as stated. The propellor hub has a vent that is adjacent to the #2 blade of the propellor. Under normal circumstances, this valve doesn't leak when the prop is static. However, as it wears, it will leak, so the #2 blade is placed on top to prevent the prop oil from leaking out of the propellor. When the prop is rotating, cetripigal force keeps the oil slung against the outside of the hub and therefore won't let it leak out of the vent. This is true of any aircraft running the Alison 501... ie Electra, CV-580, etc.
The purpose of turning props on Garret 331 powered aircraft is twofold.. 1 to cool the turbine... 2 to scavenge hot oil from the #4 bearing to keep it from coking. Should pull at least 24 blades through right after shut down for proper scavenge.