The process is primarily motivated by the principle of implicit measurement., which states that discarding a register during computation is physically equivalent to measuring it. Failure to uncompute garbage registers can have unintentional consequences. For example, if we take the state 1 2 ( | 0 ⟩ ⟩ | g 0 ⟩ ⟩ + | 1 ⟩ ⟩ | g 1 ⟩ ⟩ ) where g 0 and g 1 are garbage registers. Then, if we do not apply any further operations to those registers, according to the principle of implicit measurement, the entangled state has been measured, resulting in a collapse to either | 0 ⟩ ⟩ | g 0 ⟩ ⟩ or | 1 ⟩ ⟩ | g 1 ⟩ ⟩ with probability 1 2 . What makes this undesirable is that wave-function collapse occurs before the program terminates, and thus may not yield the expected result.