Rough-in is the stage where all the wiring goes in and none of it works yet. Boxes are mounted, cable is pulled between them, conductors are left long inside each box, and nothing is connected to a device or a fixture. Then an inspector looks at it, and only after that do the walls get closed.

The sequence exists because almost nothing about the wiring is visible once drywall is up. Box depth relative to the finished surface, cable stapling distances, protection where cable passes through framing, box fill and the routing of grounding conductors are all things that can only be checked while they are exposed.

Nail plates are a good example of why the inspection matters. Any cable running through a stud closer than an inch and a quarter to the face needs a steel plate protecting it, because that is exactly where trim screws and picture hooks end up. Once the wall is finished, the only way to discover a missing plate is for someone to hit the cable.

Box placement gets scrutinised for a similar reason. A box set too far back from the finished wall surface leaves the device unsupported and the connections exposed beyond the enclosure. A box set proud sits out past the plate. Neither is fixable without cutting drywall.

Rough-in is also the last easy moment to add anything. Running a cable for an extra receptacle, a future ceiling fan or a circuit to the garage costs very little while the framing is open and a great deal afterwards. This is the point in a project where thinking about what the room will be used for in ten years actually pays.

After the inspection passes, insulation and drywall go in, and the trim-out stage follows once surfaces are finished. That is when devices, plates and fixtures are installed and the circuits are energised and tested for the first time.

Photographing every wall before the drywall goes on is the habit worth building. A phone camera walking each room, capturing cable routes, box positions and anything unusual, produces a record that is worth a great deal the first time somebody needs to hang a cabinet or find a circuit that was never labelled properly.

Worth a read: https://registerdienste.de/