Screening simulation
While increasing the sampling for some of the molecules in the library could improve the screening accuracy, just as for a regular docking simulation, it will in general not be of interest to do a thorough sampling for each molecule in a screening, as the size of the library will make it too time consuming.
Ranking the binding of different molecules is a hard challenge for all scoring functions. A larger molecule will tend to get a higher score, due to its ability to form more interactions with the protein. It is good to keep this in mind, when studying the top scoring compounds.