Cold to Fire became a very powerful gem in 2.0. It adds a fraction of cold damage as fire damage - this directly adds to our base damage, and gets scaled by all our modifiers. Combined with Avatar of Fire, it also converts 100% of our cold damage into fire damage. This means we do a single damage type, making our penetration gem effective, and most importantly means we get to double dip on cold and fire damage increases. This makes the Snowforged node very strong, providing a full 50% increased damage. Jewels can also have both increased cold and increased fire damage, and we get the full benefit of each.