Underground utilities (such as plumbing) need to go in once sub-grade is achieved.  Footings are built along
the perimeter of a building and internally, under what will eventually be load-bearing walls.

Anchor bolts need to be placed in the forms at proper heights and locations so that the future framing (sill
plates) will be connected to the foundation.   Additionally, hold-downs need to be placed correctly at the two
termini of future shear walls, so that the loads are properly transferred down to the foundation.

Footings can precede the slab (below center) OR can coincide (below right) with it depending on the
specifics of the footings.