For normal monsters: The more players, the more drops.
For Super Uniques (like Pindleskin), Uniques and Champions: player setting is irrelevant.
Super Uniques will always drop two items.
Uniques will always drop one item.
Champions will always drop one item.
Bosses: "nodrop" will be reduced to zero for P5 (P7 for andy and duriel). In Single Player the difference between the drops for 3 player setting and 5 player setting is only marginal though (P5 for andy and duriel).