I can't put much value on rewatching many shows because so much of the enjoyment of each show relies on my not knowing what will happen or how it will happen. 

Even if I read the source material, I don't know how the adaptation will be written or acted or edited.

It's possible a 2nd viewing might completely change my view on some shows, and if that detracts from my opinion of the show, then I'd rather not rewatch it. Watching it once will preserve my memories of my initial reactions that I enjoyed so much.