If you get into a show at series 1, you have a problem. You have to wait for it to be broadcast in real time. You can't go back very far to get a hit of the old episodes while you wait. In short, it's like the olden days where nobody owned video recordings that they had bought to watch. Rubbish.
I reckon it's about series 4 where you need to get into a show. If it's reached series 4, then it's probably a show that's good and popular enough to get into. It's also matured to some sort of golden age, so watching the latest episodes is really good. Then you can go back to the now-discounted box sets of the original series and start working forwards as well.