Because you have a 42inch min cut (Frost) then you most likely will be ok in picture two. (It's 12 inches were I am)OVERDIG! That makes sense. So the main reason is efficiency and as well as the over dig area if it remains mostly undisturbed in the bigger/deeper porch allowing the soil to not have to settle then it's good and they go 42" below after the basement is backfilled for porch footings. But like @Matt1963 is saying that is assuming they do not even have to dig even further which then in turn that entire porch area would be done with the basement like the smaller porch and filled with dirt and then do the slab as usual I'm assuming since it's possible it could be in the overdig area.
Both plans do have basements and to the right are the garages.
The goal is to excavate once, pour once and backfill once. That's typically the most efficient way.Makes sense so the the bench cut area is pretty much left alone and the 2ft clear area would just be back filled and as you stated there is a 42" cut after the fact so porch can be trenched out after and either poured or cmu block. The reason behind this was to see how excavation efficiency plays a role and this can be done with budget based on design, yes.
Did you leave out "new YOUNG engineer"I spent 3 hours explaining that bridge to a new engineer one day. He made 4 phone calls before he passed it and let us pour concrete. We lost a day over that.