Growing up I always dreamed of having a clone so we could have each other's backs. If I wanted to play hookie and sneak into a movie matinee, then my clone could cover for me when I went to class. If he wanted to be a real bad boy, he could enjoy family dinners while I chilled underneath my bed and read comic books.
I never really thought about what could go wrong with that plan or my parent's inevitable discovery of my clone, but I just knew it'd be handy to have a doppelganger that I was cool with. Not the other kind of clone who wanted to have me killed and ultimately replace my life, like in Bill & Ted's Bogus Journey, that would suck.
I guess having a twin sibling is a lot like having a clone in certain situations and would be a lot more manageable than somehow materializing another version of yourself out of nowhere. If I had an identical twin brother I'm sure I could come up with some nifty uses for the circumstances of my birth.