I've found that often the DBI uses them to determine several things: Scope, number of openings, (Many charge per opening) confirm elements of Title-24, (If applicable) and scrutinize if you putting in a hidey slidey illegal unit in.
"So.... You're gonna have a storeroom with a closet and adjoining 3rd bath, and a 2nd laundry room with a sink with 2-120 circuits under it, some counter recepticals and both a 30 and a 50A dryer. And this area is going to get a new entrance from the street?"
They even get people trying to skirt condo moratoriums by slipping additional metering in. Often those people even lie to me as I'm doing the work! It often only comes out after I try beat name-plate data out of them for some wacky "Kiln" or something that will eventually become a range. Plumbers have thier clues too. A room with 2-floordains and one needs to be 4" and 15" from the wall.....
Either way they have always been reguired here for multi-trade permits to get a stamp from planning. And yes structural details are scrutinized, but in more technical ways. (Earthquake country)