You might be interested in:

$ perl -MDevel::Size=total_size -wle'
    my @a;        print total_size(\@a);
    @a=(1,2,3,4); print total_size(\@a);
    @a=();        print total_size(\@a);
'
56   <- Empty
136  <- With 4 numbers
72   <- Empty
[download]

The internal buffer of arrays and strings isn't shrunk when the array or string is shrunk in anticipation that it will grow again.

Also interesting:

$ perl -MDevel::Size=total_size -wle'
    sub foo { my @a; print total_size(\@a); @a=(1,2,3,4); }
    foo();
    foo();
'
56   <- Fresh variable
72   <- Fresh variable
[download]

Variable aren't even deallocated when they go out of scope!