Actually hes wrong. It sets up the amount of defined elements in an array.
An array in jass will always use 8192 elements. No matter if your only using 1 or 400. Its very bad to use arrays that you do not need to use. As each type in war3 uses a 4kb integer as its pointer. So you are using roughly 32kb of ram per array. Sure it doesn't seem like much but remember that types also have there own memory usage on the handling stack.