Obviously, the effect is to inform the audience but Deckard acts as if some of the information he's being given by Bryant is completely new to him, for example that they have a 4-year lifespan and that they're very hard to spot, not something you'd expect that an experienced Blade Runner would need to be told.
How could any Blade Runner not know these basic Replicant facts?
This was addressed in the Marvel Comic adaptation. In short, Rick Deckard has been out of the game for quite a few years. The last time he worked as a Blade Runner, he was taking out Nexus-3 Replicants.
Evidently those were easier to spot (albeit still disconcerting to Deckard, "too smooth, too human") and didn't have the same in-built lifespan limitations that Tyrell added to the Nexus-6 models to help cope with the fact that they're liable to go cuckoo if left to their own devices. Deckard is evidently being given new info, and presumably information that hasn't or won't be made available to the general public.
In the film's official novelisation, when we catch up with Deckard he's musing about what the latest Nexus androids would be like. It's clear that he's never encountered one.
What were they like? Deckard wondered. The newest replicants. Or reps. Or robots. Or androids. Or skin jobs. Or whatever you wanted to call them as they came off the assembly lines, each new model more lifelike than the one before.
How hard were they to control now? How hard were they to catch when they broke free? How hard were they to spot when they pre tended to be humans? How hard were they to kill?
Deckard tried to stop wondering. He stared at his raw fish. He didn't want to imagine what it would be like to off the latest model Nexus. The last runaway rep he had hunted down was a Nexus 3. Even that early model made him sick to his stomach when it went dead. It was too close to seeing a real person die. And since then the Tyrell Corporation had kept its top brains working overtime to keep offering the most lifelike humanoid slaves on the market. Aimed at people willing to take the big leap offworld, the Tyrell Nexus line was the big reason why America stayed number one in the worldwide race to settle outer space.
