The "shift" options is good to use when you send big data to the function! The process of the command is not fast, because it need to cut the value from the array, reorder the array, and create and save to a scalar variable! "shift" is good to use for big data because you don't leave in the memory the data 2 times! You just move to the scalar! If you want speed use first the @_, then if you need to change the data inside @_, you use my ($var) = @_ ;, and if you have big data you use the "shift".
"The creativity is the expression of the liberty".