Just to answer my own question: 1) The Snow melting specific cables are made tougher for in ground install such as over pavers 2) They produce a lot more heat per linear feet of wire. Generally 12watts per feet vs. 3 watts per feet for the indoor stuff.
So now lets say we were to keep the install condition the same, such as under tile and embedded into the mortar on an exterior cement slab. What would be the difference?
Okay, so we tighten the spacing of the wire a bit, maybe 1.5" separation. Then the coverage is roughly half give or take. Whatever you save would be vaporized in that scenario.
The only advantage I see is that the wire won't have to be so deep into the slab. Ideally, they want a 2" below surface install. Not something doable unless you start cutting into the slab or face it with thicker material or build it up with cement/mortar.