I’m working on a barn-style outbuilding with three large connected garage bays, with living quarters above and a kitchen/living area behind. My question is: Knowing that the connected garage bays will only be occasionally heated, should I spec sub-slab insulation under the garage floor slab?

It’s a standard build; lost the fight for exterior insulation, was able to hold on to a rainscreen gap behind the wood siding, traditional footing + stemwall foundation extending below frost line. Stem walls have exterior insulation below grade. Almost zero chance that the garage portion ever gets remodeled into habitable space; there will be a main house elsewhere on the property. 

Climate Zone 7, southwest Montana

https://www.greenbuildingadvisor.com/article/does-my-garage-need-sub-slab-insulation
Seems like it might be more wasteful to insulate than not, but was curious if anyone has another take or a best-practice for cold climates.