I am still new to all of the concrete work, but here is my understanding. If the soil has a high enough density to support the weight of the slab and structure, piers are not necessary. If the soil test finds that they are needed, piers and footers are used. here in Texas, most of the structures I have seen that have slabs have had the monolithic pour and the beams that go around the perimeter of the slab with no footer. We don't have to deal with frost heave down here, so it isn't part of the building code. They also often have beams that go underneath load bearing walls or some other heavy part of the structure. The rest of the slab for a house is usually 4 inches of reinforced concrete and 6 inches for a garage.
Water dries, rocks crumble, and trees die. The only thing that is eternal is the reputation we leave behind. - Ancient Viking Proverb
