What's the purpose of that detective role in BR?

The guy who can speak Japanese and picked up Deckard in the begining of the movie, why he seems always know Deckard 's next move, and he always be there...

This has always been a point of heated discussions. The guy's name is Gaff. And most likely, though arguably, he's there to keep an 'eye' on Harrison Ford (Rick Deckard) who is, in fact, an unaware replicant chasing replicants. The film, however, isn't too conclusive about these matters and leaves room for interpretation.

Hi,
That's a sound explanation, but dont you think this only applies to the Director's Cut where Deckard is a replicant?