sort
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OK, I will take a stab at it too. I also liked The Chinese restaurant and commend Seinfeld for taking the chance to do it.
First of all - technically it takes place in one place and in real time. What you see is what you get. Very difficult to write and to act to keep things going in that construct. So it was also an exercise in comedic TV discipline.
Second - it was similar to many *trapped* novels - I don't know enough about literature and drama to know how to explain it well but it has to do with being trapped in a situation or place. Like Alice in Wonderland, Dorothy in Oz, Poseiden Adventure, (The cult movie After Hours) and not being able to get out yet having a purpose to get out - like the movie starting soon or George's call he could not make to his girlfriend. NB: This is also similar to the episdoe The Parking Garage that many other people either love or hate too.
So there you have my take on why this was an important episode.