With so many subplots in A Midsummer Night's Dream, and so many intersections between people from different worlds, there's got to be some way to account for the different ways they each perceive reality. Dreams serve as a way to explain away plot holes or add a gauzy mystery, but the different versions of reality also extend to perspectives. In Lysander's book, if you don't have to fight for it, it isn't true love. Puck sees the mortal world as full of fools, and Theseus is certain fairies aren't real. These differing perspectives are central to the play, revealing that each man envisions his reality according to his circumstances.
Dreams are a cop-out in A Midsummer Night's Dream. They absolve the characters of responsibility for their foolishness and excuse Shakespeare from having to make the play at all sensible or meaningful.
Shakespeare makes a gendered argument in A Midsummer Night's Dream; while both Lysander and Demetrius's madness can be explained by their enchantment, Hermia and Helena have no such excuse. Shakespeare argues that women are subject to a different view of reality when it comes to love.