You may choose not to
For example, if the top two cards of your library are Brainstorm and the modal double-faced card Valki, God of Lies // Tibalt, Cosmic Imposter, you will end up with a modal double-faced card that has Brainstorm as one of its faces, and either Valki, God of Lies or Tibalt, Cosmic Imposter as the other face, with either face as the front (your choice)
A useful and rounded card but relatively low power and impact compared to many of the things you can cheat in
Decks are designed for different play styles, so they may want to match one to the type of game they prefer to play, or try something entirely different and go with the opposite of their norm
We all hide a little madness behind our sophistication, do we not? Illustrated by Cynthia Sheppard Standard Not Legal Alchemy Not Legal Pioneer Not Legal Historic Not Legal Modern Not Legal Brawl Not Legal Legacy Legal Comp
But its still a really fun card nonetheless