Unity in an artwork creates a sense of harmony and wholeness, by using similar elements within the composition and placing them in a way that brings them all together. Variety adds interest by using contrasting elements within the composition.
The plans contain the Death Star's entire design history, including the flaw introduced into its reactor system. Stolen by Jyn Erso, they are beamed to the Profundity, copied and hidden in the memory systems of a humble astromech droid.