7. Impulse Omissions
Star Trek starships are notorious for being meticulously designed to be as realistic as possible and to include as much established Trek tech as possible. Nearly all ships in the Star Trek Universe display prominent deflector dishes, lifeboat (or escape pod) hatches, airlocks, cargo and shuttlebay doors, warp engines, and impulse engines.
Unfortunately, due to the accelerated pace of the design and construction of the Romulan warbird at the end of TNG's first season, some of those little details were omitted.
While designer Andrew Probert worked diligently to include all the above components and to carefully place them in his schematics, the warbird's impulse engine fell by the wayside. According to Probert, the impulse engine was intended to be a vertical strip of lighting located at the extreme rear of the warbird:
Omitted by a tight schedule, yes, but it would have been recessed into a vertical slot starting just below that landing bay and ending symmetrically below. The reason there are few (if any) side windows at the back area of the ship is because that's where that engine and power plant would have been.
Other elements that were planned for inclusion on the Romulan warbird filming miniature but ultimately abandoned were a shuttlebay door (signified only by a small notch at rear top of the model) and a bridge window (intended for the top of head-like prow).
It's also worth noting that the Romulan warbird's primary disruptor cannon (seen firing in "The Defector", "Face of the Enemy", and numerous other episodes) was originally intended by Probert to be the ship's deflector dish, not a weapons array.