It IS needed on each drama. And several times for each episode. One or two before release of the English (depending on how quickly the English finishes and how popular the drama is), to remove sub-whining subs, another one after the English is ready, because there will still be other language sub-whiners plus of course all the remaining categories: swearwords, k-pop fandom, geo-location and time TC, inappropriate comments about the actors’ appearance, X-rated comments, repetitions (people posting the same comment about 10 times in a row), spoilers etc.
Like vaccines, it should ideally be repeated once a year thereafter.
Frankly, I feel very uneasy replying on this topic, as EVERYTHING I and all of you have said here has been repeatedly said in at least two other threads already.