sub BUFFER () { 2048 }
implements prototyping, perl's somewhat limited way of compile-time subroutine arg checking.

Doing this like shown above (the empty prototype) indicates that the sub takes no args, and if you try to pass it any args, it will produce a compile time error.

I am also somewhat sure that the difference in your compilation would be very subtle, if much different at all.

These as far as I know are considered inline subroutine constants.