Other than visual effect, the setup seems pointless.
Oh, come now. You've forgotten the all-important auditory effect of racking two slides at once. Maybe it's not quite twice as loud, but it's gotta be twice as scary, don't you think?
"Once the writer in every individual comes to life (and that time is not far off), we are in for an age of universal deafness and lack of understanding."
(Milan Kundera, Book of Laughter and Forgetting, 1980)