I started watching CID from 1998, but in the middle I didn't watch it for almost 3 years. So I missed many cases and I cannot remember some cases. This is one reason to watch the re-runs to watch the cases I haven't.
Another reason is some special moments. I can watch an episode thousand times just to listen "haan Daya", just to watch the understanding between them while defusing a bomb, just to listen ACP saying"hamara chattan jaise Daya ko kuchh nehi ho sekta" etc etc. There are so many of them.
3