The most common insufficient material scenarios are king versus king, king and bishop versus king, and king and knight versus king. In all of these cases, checkmate is impossible no matter how the pieces are arranged, so the game is automatically drawn.
King and two knights versus king is a more nuanced case: while checkmate is technically possible if the defending side cooperates by making specific moves, it cannot be forced. Some rulesets treat this as insufficient material, while others do not. Two bishops of opposite colors can deliver checkmate, so that combination is considered sufficient.
Understanding insufficient material is important for endgame play. Players should recognize when simplifying to a drawn material balance is the best practical approach, and they should avoid trading down to positions where they cannot win even with optimal play.