Police usually use Knock and Talks to talk their way into a residence with lies, manipulation, and coercion. However, this tool in the law enforcement toolbox is not always to gain entry and can be used to intimidate a suspect into making a statement that would give the officer(s) probable cause to arrest.
The one thing that you can be sure of is that if law enforcement agents are attempting a knock and talk, it's because they do not have the evidence they need to make an arrest. I can guarantee that they do not want to talk to you for any reasons that could be beneficial to you. In fact, many law enforcement careers are based on lies and the manipulation of anyone they choose to target.
As my father taught me long ago, the police are not there to help you. Arresting people is their job. There is nothing in a law enforcement officer job description that even alludes to helping people. It's all about arrest and obtaining evidence to eventually arrest.
So why on earth would anyone ever speak to a cop or investigator that knocks on their door? Well, I think back to my own case when the infamous agent Brant Rose and another agent knocked on my mother's door wanting to discuss me. Unlike me, my mother used to care about what they neighbors think. The agents at the door got louder by the minute in their attempt to get invited in. She did invite them in so no one could hear the hallway conversations. The coercive knock and talk technique worked on her. Not that she said anything at all to them once they entered, but still... they did get to have a look around.
I, on the other hand, do not give a flying crap about how loud they get in the apartment building hallway and that is where they stayed when a similar attempt was made on me around 10 days ago. No cop will ever enter anywhere I live without a search warrant. As a matter of fact, when MBI agents came to arrest me in the false and created case back in November 2001, at my home in Orange County, the first thing I stated to them at the door was that they did not have my permission to search. They screamed that I was under arrest and shoved me back inside, but they sure as hell did not get the benefit of searching!
So to conclude here: Knock and talks can be utilized by law enforcement to gain entry to a residence or just to talk to a person or a suspect to get information they will later use to arrest. What we do know for sure is that cops do not bother with knock and talks if they have evidence (probable cause) to arrest - they simply arrest and then attempt to manipulate the party into a statement while in custody - because in-custody manipulation is so much easier for them.
If law enforcement officers ever show-up at your door attempting a knock and talk, call an attorney. After all is said and done, we have few rights left in this country, but we always have the right to shut-up and not hand them what they need to get an arrest warrant. Words can be twisted and conversations manipulated and they're definitely not stopping by to help you.