In previous SimCity's, the grid controlled spacing and orientation. In the new one, that job is handled by roads. You use roads to structure your city, to space and orient your buildings, to set up transportation networks and to give it shape.
Pedestrians walk on roads, cars, trucks and service vehicles drive on them. Power is carried by them, sewage and water travel under them. Buildings are snapped and oriented to them. Roads are the connective tissue for your city.