Rough-in is electrical work done before the walls are closed. Every outlet box, switch box and light fixture has to be positioned relative to the finished wall — including tile, waterproofing, adhesive, and all the layers that will exist between the structure and what you see. The box face has to sit flush with that finished surface. Too shallow and it sticks out past the tile. Too deep and it is recessed inside the tile, creating a gap where water can sit behind the tile.
The depth is calculated before any boarding goes up. Board thickness, tile thickness, adhesive, and waterproofing membranes — they all add up. A 1/2-inch drywall, a layer of waterproofing membrane, 3/8-inch cement board, thin-set mortar, and 3/8-inch tile is already 1.5 inches of finish layers. The box face has to be set for that total depth so the trim sits flush. If the wall build-up changes — say, thinner tile or a thicker board than originally planned — the boxes are now at the wrong depth and the trim will not sit properly. A box set too shallow creates a gap at the edge where the trim cannot hide it. A box set too deep ends up recessed inside the tile, creating a dead space behind the tile where moisture can collect.
Box positions are set against the fittings actually chosen, not generic locations or standard heights. A vanity light might nominally go at 60 inches, but the actual vanity ordered might have its light fixture positioned at 54 inches or 66 inches depending on the design. The outlet boxes should be positioned for the exact fixtures being installed, not a standard height assumption. That requires the fixtures and cabinetry to be chosen and confirmed before rough-in happens. This is why the design and specification phase comes before the electrical rough-in work.
A draw wire installed while the wall is open provides a future path for adding cable or small pipes without opening the wall later. If it is anticipated that future work might need a new run through a finished wall — for a future outlet, a new light, or future plumbing — a conduit or draw wire installed now is the only way to make that future work possible. Once the wall is closed and the tile is installed, installing anything new is blind work and guesswork, requiring wall demolition to install cable. Installing a draw wire now is cheap planning that pays off later.