The turf covers used on the greens are made of a breathable fabric that allows for sun and water infiltration while keeping the surface under the tarp warmer than the air above it.
There are many benefits for using covers such as, reduces winter kill, earlier green up, reduces fertilizer evaporation, and promotes healthy roots. Those are all great reasons to use covers from an agronomics point of view, but the main reason we cover greens #3, #4 and #6 is to keep the geese from picking at the turf during the January thaws.
Those greens seem to melt off much quicker than any other spot on the course, so they become quite vulnerable to the ferocious appetite of hungry geese. Unfortunately, not everyone settles down for a long winters nap!