OK, you have probably many times seen icicles hanging from the soffit of older homes.  What causes this ? Well,  it is the action of the base of the soffit being warmer than that of the exterior ambient air from internal temperature of the home.   Also, little or no external air flow exists from the soffit to the roof vents near the top of the roof.   Soffit vents promote attic ventilation and effectively reduce the  probability of ice damming.  Ice damming is where the snow or ice forms at the base of the roof overhang; this in turn creeps up and under the roof shingles, resulting in premature wear of shingles and roof structure.  Recommendation is to install or remove obstructions from soffit vents underside of the roof structure and allow the exterior air to enter the attic and exit the roof vents.  This keeps the attic internal air temperature at approx. the same as that of the ambient exterior air.  Therefore no more thawing or heating at the base of the roof shingles and structure.  Generally not a high cost item to repair, but essential to have it done.