Layout wiring can be as simple or as complex as you need for it to be. Theoretically, all you need to do is connect two wires from the booster to the track, and, except for reverse sections, it will work. But we all know that most railroads need several sets of track feeders to operate smoothly throughout the entire track plan.
Nickel silver track is not a good conductor of electricity. Further, rail joiners can create a potential for interruption of power. So, you need to have track power feeders every six to ten feet. Even so, it’s still just two wires strung around the layout for feeders to be connected to the track in several places.
However, there are other things that can cause more complexity than this, such as reverse polarity sections, additional boosters to run more trains, additional boosters to isolate derailments from affecting other trains, and detection blocking for train position or signaling. But in all cases, it is always easier wiring DCC than it is for block control. The fact that you don’t have to wire all those toggle switches makes this self evident.
Even though the electrical polarity on the rail does not control the direction of the loco, you still have to contend with reverse sections. After all, if the track turns around back onto itself, the right rail will come in contact with the left rail. And that is a short circuit, the same as placing a metal object across the rails. Reverse sections are discussed at length in the section called Reverse Section Control.