The scalar also contains less information, and the process is NOT generally reversible.
It is quite easy to reduce the memory use when your algorithm is allowed to be lossy :)

For example, consider my @array = (1, 5, "hello,world!", 3.1415);
There is no way to restore the original array after doing a join ',',@array on it.
"1,5,hello,world!,3.1415" could have been (1, 5, "hello,world!", 3.1415) or it could have been (1, 5, "hello", "world!", 3.1415).