The concepts of QN vs QB in chess refer to a comparison between two different piece combinations: a queen and knight (QN) and a queen and bishop (QB). Both combinations have their strengths and weaknesses, and the choice between them often depends on the specific situation and position of the pieces on the board. Having a QN combination can provide a player with greater mobility and control over the board. Knights are particularly effective in certain positions, such as when they are placed on outposts or when they are used to attack the opponent's pawn structure. On the other hand, the QB combination can be more effective in controlling the center of the board and exerting pressure on the opponent's pieces.