"You have to settle for less" puzzle

 

AHA, for that last one you probably weren't expecting that!  One of the uses of under-promotion is also to avoid a situation like stalemate.  Although the most common promotions are the queens and knights (because knights have a different movement pattern than a queen), it is not like the other promotions are completely useless.  Even though the queen embodies a rook or a bishop, stalemate comes from one person being so powerful that they restrict their opponent to nothing.  Sometimes, that power needs to be limited, so in the case of promotion, a lesser form of the queen (bishop and rook) would need to be used.