I watched this video (building a free-standing porch) and wondered what is the reason that the back concrete blocks are not tight to the house wall. Basically he places them away from the house by a few inches.
The finished exterior wall is out from the concrete foundation somewhat. If the footing blocks were set tight to the foundation, there would be no room for the rim joists that wrap around the posts.
There are a lot of things you will need to do with the exterior wall. Eventually, there will be paint, siding replacement, etc.
Modern decks are more and more required to support themselves - that is, not to try to transfer any weight to the wall of the house. If you're doing that, it doesn't matter where the footings go, so long as the edge of the deck ends up very near the wall, and the deck is stable.
So why not make it easy(-ier) to do maintenance on the house, proper?