Little to none. Just someone to scan, a name, a picture, that's it.
Surliat, the reason why Adfeng said this is to prevent AOL, which is to say Analytical OverLay. In other words, you mix your own beliefs with actual information you are gaining from the target, thus decreasing ones accuracy. Like Adfeng said, you pretty much need only those three things mentioned above ^. Any more and it would be front-loading the RVer (front-loading is kind of like encouraging AOL to occur).