Its definitely to prevent ice damns. We can go ten years without a problem then the right combination of snow , and warm/cold nights and you get one. Interestingly it has only ever happened on the front of my house. back roof is same but i don't get it there. i think its cause the back is always in shade so it doesn't melt and refreeze each night.
The only other alternative for me was to attach a piece of plywood to a long 2x 4 and i rake the snow off the last foot or two.
i wouldn't worry about it. the fact you have the heaters up there means its been addressed in the past.
i think the newer codes require a sheet of asphalt impregnated cloth for the first 3 to 4 feet so even if the melting and freezing occurs , the water won't climb up past it to get in.
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