It is an optional cold climate thing. Especially if you remove snow in some area of the concrete but not everywhere. Snow as strange at it seems provide insulation so the ground do not freeze at the same depth level with or without snow. This mean that your concrete will play differently which you do not want to avoid cracks. Also this insulation keep the water away from the concrete. A slab without insulation will move up in some area which could also be a problem for shed door for example.That’s looking great!
Ok, gonna show my ignorance here… what’s the under slab insulation for? I’ve seen that done when installing radiant floor heating, but never outdoors.
For reference basement / wall insulation is mandatory in Canada / Quebec construction code since 2012. But still I doubt there is a lot of people doing what I do to 1100 square ft of patio...