Minecraft wiki entry for Snow_golems, associated text: Requires fewer golems.
Kills monsters, eliminating them as threats to the player.
Skeletons have less time to shoot arrows, resulting in a longer life span per golem.
More effective against a slow, steady number of monsters, and if defending all night.
More useful if the player is not attending it.
If it leads to a mob trap, the drops can be collected.